diff --git a/fastNLP/core/README.md b/fastNLP/core/README.md
deleted file mode 100644
index 8b137891..00000000
--- a/fastNLP/core/README.md
+++ /dev/null
@@ -1 +0,0 @@
-
diff --git a/fastNLP/core/action.py b/fastNLP/core/action.py
index ef595cbb..c6cf2d63 100644
--- a/fastNLP/core/action.py
+++ b/fastNLP/core/action.py
@@ -4,88 +4,6 @@ import numpy as np
 import torch
 
 
-class Action(object):
-    """Operations shared by Trainer, Tester, or Inference.
-
-        This is designed for reducing replicate codes.
-            - make_batch: produce a min-batch of data. @staticmethod
-            - pad: padding method used in sequence modeling. @staticmethod
-            - mode: change network mode for either train or test. (for PyTorch) @staticmethod
-    """
-
-    def __init__(self):
-        super(Action, self).__init__()
-
-    @staticmethod
-    def make_batch(iterator, use_cuda, output_length=True, max_len=None):
-        """Batch and Pad data.
-
-        :param iterator: an iterator, (object that implements __next__ method) which returns the next sample.
-        :param use_cuda: bool, whether to use GPU
-        :param output_length: bool, whether to output the original length of the sequence before padding. (default: True)
-        :param max_len: int, maximum sequence length. Longer sequences will be clipped. (default: None)
-        :return :
-
-        if output_length is True,
-            (batch_x, seq_len): tuple of two elements
-                     batch_x: list. Each entry is a list of features of a sample. [batch_size, max_len]
-                     seq_len: list. The length of the pre-padded sequence, if output_length is True.
-            batch_y: list. Each entry is a list of labels of a sample.  [batch_size, num_labels]
-
-        if output_length is False,
-            batch_x: list. Each entry is a list of features of a sample. [batch_size, max_len]
-            batch_y: list. Each entry is a list of labels of a sample.  [batch_size, num_labels]
-        """
-        for batch in iterator:
-            batch_x = [sample[0] for sample in batch]
-            batch_y = [sample[1] for sample in batch]
-
-            batch_x = Action.pad(batch_x)
-            # pad batch_y only if it is a 2-level list
-            if len(batch_y) > 0 and isinstance(batch_y[0], list):
-                batch_y = Action.pad(batch_y)
-
-            # convert list to tensor
-            batch_x = convert_to_torch_tensor(batch_x, use_cuda)
-            batch_y = convert_to_torch_tensor(batch_y, use_cuda)
-
-            # trim data to max_len
-            if max_len is not None and batch_x.size(1) > max_len:
-                batch_x = batch_x[:, :max_len]
-
-            if output_length:
-                seq_len = [len(x) for x in batch_x]
-                yield (batch_x, seq_len), batch_y
-            else:
-                yield batch_x, batch_y
-
-    @staticmethod
-    def pad(batch, fill=0):
-        """ Pad a mini-batch of sequence samples to maximum length of this batch.
-
-        :param batch: list of list
-        :param fill: word index to pad, default 0.
-        :return batch: a padded mini-batch
-        """
-        max_length = max([len(x) for x in batch])
-        for idx, sample in enumerate(batch):
-            if len(sample) < max_length:
-                batch[idx] = sample + ([fill] * (max_length - len(sample)))
-        return batch
-
-    @staticmethod
-    def mode(model, is_test=False):
-        """Train mode or Test mode. This is for PyTorch currently.
-
-        :param model: a PyTorch model
-        :param is_test: bool, whether in test mode or not.
-        """
-        if is_test:
-            model.eval()
-        else:
-            model.train()
-
-
 def convert_to_torch_tensor(data_list, use_cuda):
     """Convert lists into (cuda) Tensors.
 
@@ -168,19 +86,7 @@ class BaseSampler(object):
 
     """
 
-    def __init__(self, data_set):
-        """
-
-        :param data_set: multi-level list, of shape [num_example, *]
-
-        """
-        self.data_set_length = len(data_set)
-        self.data = data_set
-
-    def __len__(self):
-        return self.data_set_length
-
-    def __iter__(self):
+    def __call__(self, *args, **kwargs):
         raise NotImplementedError
 
 
@@ -189,16 +95,8 @@ class SequentialSampler(BaseSampler):
 
     """
 
-    def __init__(self, data_set):
-        """
-
-        :param data_set: multi-level list
-
-        """
-        super(SequentialSampler, self).__init__(data_set)
-
-    def __iter__(self):
-        return iter(self.data)
+    def __call__(self, data_set):
+        return list(range(len(data_set)))
 
 
 class RandomSampler(BaseSampler):
@@ -206,17 +104,9 @@ class RandomSampler(BaseSampler):
 
     """
 
-    def __init__(self, data_set):
-        """
+    def __call__(self, data_set):
+        return list(np.random.permutation(len(data_set)))
 
-        :param data_set: multi-level list
-
-        """
-        super(RandomSampler, self).__init__(data_set)
-        self.order = np.random.permutation(self.data_set_length)
-
-    def __iter__(self):
-        return iter((self.data[idx] for idx in self.order))
 
 
 class Batchifier(object):
@@ -252,6 +142,7 @@ class BucketBatchifier(Batchifier):
     """Partition all samples into multiple buckets, each of which contains sentences of approximately the same length.
     In sampling, first random choose a bucket. Then sample data from it.
     The number of buckets is decided dynamically by the variance of sentence lengths.
+    TODO: merge it into Batch
     """
 
     def __init__(self, data_set, batch_size, num_buckets, drop_last=True, sampler=None):
diff --git a/fastNLP/core/batch.py b/fastNLP/core/batch.py
new file mode 100644
index 00000000..0a5e9712
--- /dev/null
+++ b/fastNLP/core/batch.py
@@ -0,0 +1,126 @@
+from collections import defaultdict
+
+import torch
+
+from fastNLP.core.dataset import DataSet
+from fastNLP.core.field import TextField, LabelField
+from fastNLP.core.instance import Instance
+
+
+class Batch(object):
+    """Batch is an iterable object which iterates over mini-batches.
+
+    ::
+        for batch_x, batch_y in Batch(data_set):
+
+    """
+
+    def __init__(self, dataset, batch_size, sampler, use_cuda):
+        self.dataset = dataset
+        self.batch_size = batch_size
+        self.sampler = sampler
+        self.use_cuda = use_cuda
+        self.idx_list = None
+        self.curidx = 0
+
+    def __iter__(self):
+        self.idx_list = self.sampler(self.dataset)
+        self.curidx = 0
+        self.lengths = self.dataset.get_length()
+        return self
+
+    def __next__(self):
+        """
+
+        :return batch_x: dict of (str: torch.LongTensor), which means (field name: tensor of shape [batch_size, padding_length])
+                         batch_x also contains an item (str: list of int) about origin lengths,
+                         which means ("field_name_origin_len": origin lengths).
+                         E.g.
+                         ::
+                         {'text': tensor([[ 0,  1,  2,  3,  0,  0,  0], 4,  5,  2,  6,  7,  8,  9]]), 'text_origin_len': [4, 7]})
+
+                batch_y: dict of (str: torch.LongTensor), which means (field name: tensor of shape [batch_size, padding_length])
+                All tensors in both batch_x and batch_y will be cuda tensors if use_cuda is True.
+                The names of fields are defined in preprocessor's convert_to_dataset method.
+
+        """
+        if self.curidx >= len(self.idx_list):
+            raise StopIteration
+        else:
+            endidx = min(self.curidx + self.batch_size, len(self.idx_list))
+            padding_length = {field_name: max(field_length[self.curidx: endidx])
+                              for field_name, field_length in self.lengths.items()}
+            origin_lengths = {field_name: field_length[self.curidx: endidx]
+                              for field_name, field_length in self.lengths.items()}
+
+            batch_x, batch_y = defaultdict(list), defaultdict(list)
+            for idx in range(self.curidx, endidx):
+                x, y = self.dataset.to_tensor(idx, padding_length)
+                for name, tensor in x.items():
+                    batch_x[name].append(tensor)
+                for name, tensor in y.items():
+                    batch_y[name].append(tensor)
+
+            batch_origin_length = {}
+            # combine instances into a batch
+            for batch in (batch_x, batch_y):
+                for name, tensor_list in batch.items():
+                    if self.use_cuda:
+                        batch[name] = torch.stack(tensor_list, dim=0).cuda()
+                    else:
+                        batch[name] = torch.stack(tensor_list, dim=0)
+
+            # add origin lengths in batch_x
+            for name, tensor in batch_x.items():
+                if self.use_cuda:
+                    batch_origin_length[name + "_origin_len"] = torch.LongTensor(origin_lengths[name]).cuda()
+                else:
+                    batch_origin_length[name + "_origin_len"] = torch.LongTensor(origin_lengths[name])
+            batch_x.update(batch_origin_length)
+
+            self.curidx += endidx
+            return batch_x, batch_y
+
+
+if __name__ == "__main__":
+    """simple running example
+    """
+    texts = ["i am a cat",
+             "this is a test of new batch",
+             "haha"
+             ]
+    labels = [0, 1, 0]
+
+    # prepare vocabulary
+    vocab = {}
+    for text in texts:
+        for tokens in text.split():
+            if tokens not in vocab:
+                vocab[tokens] = len(vocab)
+    print("vocabulary: ", vocab)
+
+    # prepare input dataset    
+    data = DataSet()
+    for text, label in zip(texts, labels):
+        x = TextField(text.split(), False)
+        y = LabelField(label, is_target=True)
+        ins = Instance(text=x, label=y)
+        data.append(ins)
+
+    # use vocabulary to index data
+    data.index_field("text", vocab)
+
+
+    # define naive sampler for batch class
+    class SeqSampler:
+        def __call__(self, dataset):
+            return list(range(len(dataset)))
+
+
+    # use batch to iterate dataset
+    data_iterator = Batch(data, 2, SeqSampler(), False)
+    for epoch in range(1):
+        for batch_x, batch_y in data_iterator:
+            print(batch_x)
+            print(batch_y)
+            # do stuff
diff --git a/fastNLP/core/dataset.py b/fastNLP/core/dataset.py
new file mode 100644
index 00000000..bb1a1890
--- /dev/null
+++ b/fastNLP/core/dataset.py
@@ -0,0 +1,111 @@
+from collections import defaultdict
+
+from fastNLP.core.field import TextField
+from fastNLP.core.instance import Instance
+
+
+def create_dataset_from_lists(str_lists: list, word_vocab: dict, has_target: bool = False, label_vocab: dict = None):
+    if has_target is True:
+        if label_vocab is None:
+            raise RuntimeError("Must provide label vocabulary to transform labels.")
+        return create_labeled_dataset_from_lists(str_lists, word_vocab, label_vocab)
+    else:
+        return create_unlabeled_dataset_from_lists(str_lists, word_vocab)
+
+
+def create_labeled_dataset_from_lists(str_lists, word_vocab, label_vocab):
+    """Create an DataSet instance that contains labels.
+
+    :param str_lists: list of list of strings, [num_examples, 2, *].
+            ::
+            [
+                [[word_11, word_12, ...], [label_11, label_12, ...]],
+                ...
+            ]
+
+    :param word_vocab: dict of (str: int), which means (word: index).
+    :param label_vocab: dict of (str: int), which means (word: index).
+    :return data_set: a DataSet instance.
+
+    """
+    data_set = DataSet()
+    for example in str_lists:
+        word_seq, label_seq = example[0], example[1]
+        x = TextField(word_seq, is_target=False)
+        y = TextField(label_seq, is_target=True)
+        data_set.append(Instance(word_seq=x, label_seq=y))
+    data_set.index_field("word_seq", word_vocab)
+    data_set.index_field("label_seq", label_vocab)
+    return data_set
+
+
+def create_unlabeled_dataset_from_lists(str_lists, word_vocab):
+    """Create an DataSet instance that contains no labels.
+
+    :param str_lists: list of list of strings, [num_examples, *].
+            ::
+            [
+                [word_11, word_12, ...],
+                ...
+            ]
+
+    :param word_vocab: dict of (str: int), which means (word: index).
+    :return data_set: a DataSet instance.
+
+    """
+    data_set = DataSet()
+    for word_seq in str_lists:
+        x = TextField(word_seq, is_target=False)
+        data_set.append(Instance(word_seq=x))
+    data_set.index_field("word_seq", word_vocab)
+    return data_set
+
+
+class DataSet(list):
+    """A DataSet object is a list of Instance objects.
+
+    """
+    def __init__(self, name="", instances=None):
+        """
+
+        :param name: str, the name of the dataset. (default: "")
+        :param instances: list of Instance objects. (default: None)
+
+        """
+        list.__init__([])
+        self.name = name
+        if instances is not None:
+            self.extend(instances)
+
+    def index_all(self, vocab):
+        for ins in self:
+            ins.index_all(vocab)
+
+    def index_field(self, field_name, vocab):
+        for ins in self:
+            ins.index_field(field_name, vocab)
+
+    def to_tensor(self, idx: int, padding_length: dict):
+        """Convert an instance in a dataset to tensor.
+
+        :param idx: int, the index of the instance in the dataset.
+        :param padding_length: int
+        :return tensor_x: dict of (str: torch.LongTensor), which means (field name: tensor of shape [padding_length, ])
+                tensor_y: dict of (str: torch.LongTensor), which means (field name: tensor of shape [padding_length, ])
+
+        """
+        ins = self[idx]
+        return ins.to_tensor(padding_length)
+
+    def get_length(self):
+        """Fetch lengths of all fields in all instances in a dataset.
+
+        :return lengths: dict of (str: list). The str is the field name.
+                The list contains lengths of this field in all instances.
+
+        """
+        lengths = defaultdict(list)
+        for ins in self:
+            for field_name, field_length in ins.get_length().items():
+                lengths[field_name].append(field_length)
+        return lengths
diff --git a/fastNLP/core/field.py b/fastNLP/core/field.py
new file mode 100644
index 00000000..f5347bd6
--- /dev/null
+++ b/fastNLP/core/field.py
@@ -0,0 +1,93 @@
+import torch
+
+
+class Field(object):
+    """A field defines a data type.
+
+    """
+
+    def __init__(self, is_target: bool):
+        self.is_target = is_target
+
+    def index(self, vocab):
+        raise NotImplementedError
+
+    def get_length(self):
+        raise NotImplementedError
+
+    def to_tensor(self, padding_length):
+        raise NotImplementedError
+
+
+class TextField(Field):
+    def __init__(self, text, is_target):
+        """
+        :param text: list of strings
+        :param is_target: bool
+        """
+        super(TextField, self).__init__(is_target)
+        self.text = text
+        self._index = None
+
+    def index(self, vocab):
+        if self._index is None:
+            self._index = [vocab[c] for c in self.text]
+        else:
+            raise RuntimeError("Replicate indexing of this field.")
+        return self._index
+
+    def get_length(self):
+        """Fetch the length of the text field.
+
+        :return length: int, the length of the text.
+
+        """
+        return len(self.text)
+
+    def to_tensor(self, padding_length: int):
+        """Convert text field to tensor.
+
+        :param padding_length: int
+        :return tensor: torch.LongTensor, of shape [padding_length, ]
+        """
+        pads = []
+        if self._index is None:
+            raise RuntimeError("Indexing not done before to_tensor in TextField.")
+        if padding_length > self.get_length():
+            pads = [0] * (padding_length - self.get_length())
+        return torch.LongTensor(self._index + pads)
+
+
+class LabelField(Field):
+    def __init__(self, label, is_target=True):
+        super(LabelField, self).__init__(is_target)
+        self.label = label
+        self._index = None
+
+    def get_length(self):
+        """Fetch the length of the label field.
+
+        :return length: int, the length of the label, always 1.
+        """
+        return 1
+
+    def index(self, vocab):
+        if self._index is None:
+            self._index = vocab[self.label]
+        return self._index
+
+    def to_tensor(self, padding_length):
+        if self._index is None:
+            if isinstance(self.label, int):
+                return torch.LongTensor([self.label])
+            elif isinstance(self.label, str):
+                raise RuntimeError("Field {} not indexed. Call index method.".format(self.label))
+            else:
+                raise RuntimeError(
+                    "Not support type for LabelField. Expect str or int, got {}.".format(type(self.label)))
+        else:
+            return torch.LongTensor([self._index])
+
+
+if __name__ == "__main__":
+    tf = TextField("test the code".split(), is_target=False)
diff --git a/fastNLP/core/instance.py b/fastNLP/core/instance.py
new file mode 100644
index 00000000..32f95197
--- /dev/null
+++ b/fastNLP/core/instance.py
@@ -0,0 +1,53 @@
+class Instance(object):
+    """An instance which consists of Fields is an example in the DataSet.
+
+    """
+
+    def __init__(self, **fields):
+        self.fields = fields
+        self.has_index = False
+        self.indexes = {}
+
+    def add_field(self, field_name, field):
+        self.fields[field_name] = field
+
+    def get_length(self):
+        """Fetch the length of all fields in the instance.
+
+        :return length: dict of (str: int), which means (field name: field length).
+
+        """
+        length = {name: field.get_length() for name, field in self.fields.items()}
+        return length
+
+    def index_field(self, field_name, vocab):
+        """use `vocab` to index certain field
+        """
+        self.indexes[field_name] = self.fields[field_name].index(vocab)
+
+    def index_all(self, vocab):
+        """use `vocab` to index all fields
+        """
+        if self.has_index:
+            print("error")
+            return self.indexes
+        indexes = {name: field.index(vocab) for name, field in self.fields.items()}
+        self.indexes = indexes
+        return indexes
+
+    def to_tensor(self, padding_length: dict):
+        """Convert instance to tensor.
+
+        :param padding_length: dict of (str: int), which means (field name: padding_length of this field)
+        :return tensor_x: dict of (str: torch.LongTensor), which means (field name: tensor of shape [padding_length, ])
+                tensor_y: dict of (str: torch.LongTensor), which means (field name: tensor of shape [padding_length, ])
+                        If is_target is False for all fields, tensor_y would be an empty dict.
+        """
+        tensor_x = {}
+        tensor_y = {}
+        for name, field in self.fields.items():
+            if field.is_target:
+                tensor_y[name] = field.to_tensor(padding_length[name])
+            else:
+                tensor_x[name] = field.to_tensor(padding_length[name])
+        return tensor_x, tensor_y
diff --git a/fastNLP/core/predictor.py b/fastNLP/core/predictor.py
index d04a6ef0..802661ef 100644
--- a/fastNLP/core/predictor.py
+++ b/fastNLP/core/predictor.py
@@ -1,53 +1,10 @@
 import numpy as np
 import torch
 
-from fastNLP.core.action import Batchifier, SequentialSampler
-from fastNLP.core.action import convert_to_torch_tensor
-from fastNLP.core.preprocess import load_pickle, DEFAULT_UNKNOWN_LABEL
-from fastNLP.modules import utils
-
-
-def make_batch(iterator, use_cuda, output_length=False, max_len=None, min_len=None):
-    """Batch and Pad data, only for Inference.
-
-    :param iterator: An iterable object that returns a list of indices representing a mini-batch of samples.
-    :param use_cuda: bool, whether to use GPU
-    :param output_length: bool, whether to output the original length of the sequence before padding. (default: False)
-    :param max_len: int, maximum sequence length. Longer sequences will be clipped. (default: None)
-    :param min_len: int, minimum sequence length. Shorter sequences will be padded. (default: None)
-    :return:
-    """
-    for batch_x in iterator:
-        batch_x = pad(batch_x)
-        # convert list to tensor
-        batch_x = convert_to_torch_tensor(batch_x, use_cuda)
-
-        # trim data to max_len
-        if max_len is not None and batch_x.size(1) > max_len:
-            batch_x = batch_x[:, :max_len]
-        if min_len is not None and batch_x.size(1) < min_len:
-            pad_tensor = torch.zeros(batch_x.size(0), min_len - batch_x.size(1)).to(batch_x)
-            batch_x = torch.cat((batch_x, pad_tensor), 1)
-
-        if output_length:
-            seq_len = [len(x) for x in batch_x]
-            yield tuple([batch_x, seq_len])
-        else:
-            yield batch_x
-
-
-def pad(batch, fill=0):
-    """ Pad a mini-batch of sequence samples to maximum length of this batch.
-
-    :param batch: list of list
-    :param fill: word index to pad, default 0.
-    :return batch: a padded mini-batch
-    """
-    max_length = max([len(x) for x in batch])
-    for idx, sample in enumerate(batch):
-        if len(sample) < max_length:
-            batch[idx] = sample + ([fill] * (max_length - len(sample)))
-    return batch
+from fastNLP.core.action import SequentialSampler
+from fastNLP.core.batch import Batch
+from fastNLP.core.dataset import create_dataset_from_lists
+from fastNLP.core.preprocess import load_pickle
 
 
 class Predictor(object):
@@ -59,11 +16,17 @@ class Predictor(object):
     Currently, Predictor does not support GPU.
     """
 
-    def __init__(self, pickle_path):
+    def __init__(self, pickle_path, task):
+        """
+
+        :param pickle_path: str, the path to the pickle files.
+        :param task: str, specify which task the predictor will perform. One of ("seq_label", "text_classify").
+
+        """
         self.batch_size = 1
         self.batch_output = []
-        self.iterator = None
         self.pickle_path = pickle_path
+        self._task = task  # one of ("seq_label", "text_classify")
         self.index2label = load_pickle(self.pickle_path, "id2class.pkl")
         self.word2index = load_pickle(self.pickle_path, "word2id.pkl")
 
@@ -71,19 +34,19 @@ class Predictor(object):
         """Perform inference using the trained model.
 
         :param network: a PyTorch model (cpu)
-        :param data: list of list of strings
+        :param data: list of list of strings, [num_examples, seq_len]
         :return: list of list of strings, [num_examples, tag_seq_length]
         """
-        # transform strings into indices
+        # transform strings into DataSet object
         data = self.prepare_input(data)
 
         # turn on the testing mode; clean up the history
         self.mode(network, test=True)
         self.batch_output.clear()
 
-        data_iterator = iter(Batchifier(SequentialSampler(data), self.batch_size, drop_last=False))
+        data_iterator = Batch(data, batch_size=self.batch_size, sampler=SequentialSampler(), use_cuda=False)
 
-        for batch_x in self.make_batch(data_iterator, use_cuda=False):
+        for batch_x, _ in data_iterator:
             with torch.no_grad():
                 prediction = self.data_forward(network, batch_x)
 
@@ -99,103 +62,61 @@ class Predictor(object):
 
     def data_forward(self, network, x):
         """Forward through network."""
-        raise NotImplementedError
-
-    def make_batch(self, iterator, use_cuda):
-        raise NotImplementedError
+        y = network(**x)
+        if self._task == "seq_label":
+            y = network.prediction(y)
+        return y
 
     def prepare_input(self, data):
-        """Transform two-level list of strings into that of index.
+        """Transform two-level list of strings into an DataSet object.
+        In the training pipeline, this is done by Preprocessor. But in inference time, we do not call Preprocessor.
 
-        :param data:
+        :param data: list of list of strings.
+                ::
                 [
                     [word_11, word_12, ...],
                     [word_21, word_22, ...],
                     ...
                 ]
-        :return data_index: list of list of int.
+
+        :return data_set: a DataSet instance.
         """
         assert isinstance(data, list)
-        data_index = []
-        default_unknown_index = self.word2index[DEFAULT_UNKNOWN_LABEL]
-        for example in data:
-            data_index.append([self.word2index.get(w, default_unknown_index) for w in example])
-        return data_index
+        return create_dataset_from_lists(data, self.word2index, has_target=False)
 
     def prepare_output(self, data):
         """Transform list of batch outputs into strings."""
-        raise NotImplementedError
+        if self._task == "seq_label":
+            return self._seq_label_prepare_output(data)
+        elif self._task == "text_classify":
+            return self._text_classify_prepare_output(data)
+        else:
+            raise NotImplementedError("Unknown task type {}".format(self._task))
 
-
-class SeqLabelInfer(Predictor):
-    """
-    Inference on sequence labeling models.
-    """
-
-    def __init__(self, pickle_path):
-        super(SeqLabelInfer, self).__init__(pickle_path)
-
-    def data_forward(self, network, inputs):
-        """
-        This is only for sequence labeling with CRF decoder.
-        :param network: a PyTorch model
-        :param inputs: tuple of (x, seq_len)
-                        x: Tensor of shape [batch_size, max_len], where max_len is the maximum length of the mini-batch
-                            after padding.
-                        seq_len: list of int, the lengths of sequences before padding.
-        :return prediction: Tensor of shape [batch_size, max_len]
-        """
-        if not isinstance(inputs[1], list) and isinstance(inputs[0], list):
-            raise RuntimeError("output_length must be true for sequence modeling.")
-        # unpack the returned value from make_batch
-        x, seq_len = inputs[0], inputs[1]
-        batch_size, max_len = x.size(0), x.size(1)
-        mask = utils.seq_mask(seq_len, max_len)
-        mask = mask.byte().view(batch_size, max_len)
-        y = network(x)
-        prediction = network.prediction(y, mask)
-        return torch.Tensor(prediction)
-
-    def make_batch(self, iterator, use_cuda):
-        return make_batch(iterator, use_cuda, output_length=True)
-
-    def prepare_output(self, batch_outputs):
-        """Transform list of batch outputs into strings.
-
-        :param batch_outputs: list of 2-D Tensor, shape [num_batch, batch-size, tag_seq_length].
-        :return results: 2-D list of strings, shape [num_examples, tag_seq_length]
-        """
+    def _seq_label_prepare_output(self, batch_outputs):
         results = []
         for batch in batch_outputs:
             for example in np.array(batch):
                 results.append([self.index2label[int(x)] for x in example])
         return results
 
-
-class ClassificationInfer(Predictor):
-    """
-    Inference on Classification models.
-    """
-
-    def __init__(self, pickle_path):
-        super(ClassificationInfer, self).__init__(pickle_path)
-
-    def data_forward(self, network, x):
-        """Forward through network."""
-        logits = network(x)
-        return logits
-
-    def make_batch(self, iterator, use_cuda):
-        return make_batch(iterator, use_cuda, output_length=False, min_len=5)
-
-    def prepare_output(self, batch_outputs):
-        """
-        Transform list of batch outputs into strings.
-        :param batch_outputs: list of 2-D Tensor, of shape [num_batch, batch-size, num_classes].
-        :return results: list of strings
-        """
+    def _text_classify_prepare_output(self, batch_outputs):
         results = []
         for batch_out in batch_outputs:
             idx = np.argmax(batch_out.detach().numpy(), axis=-1)
             results.extend([self.index2label[i] for i in idx])
         return results
+
+
+class SeqLabelInfer(Predictor):
+    def __init__(self, pickle_path):
+        print(
+            "[FastNLP Warning] SeqLabelInfer will be deprecated. Please use Predictor with argument 'task'='seq_label'.")
+        super(SeqLabelInfer, self).__init__(pickle_path, "seq_label")
+
+
+class ClassificationInfer(Predictor):
+    def __init__(self, pickle_path):
+        print(
+            "[FastNLP Warning] ClassificationInfer will be deprecated. Please use Predictor with argument 'task'='text_classify'.")
+        super(ClassificationInfer, self).__init__(pickle_path, "text_classify")
diff --git a/fastNLP/core/preprocess.py b/fastNLP/core/preprocess.py
index 5e4122f9..b5d348e6 100644
--- a/fastNLP/core/preprocess.py
+++ b/fastNLP/core/preprocess.py
@@ -3,6 +3,10 @@ import os
 
 import numpy as np
 
+from fastNLP.core.dataset import DataSet
+from fastNLP.core.field import TextField, LabelField
+from fastNLP.core.instance import Instance
+
 DEFAULT_PADDING_LABEL = '<pad>'  # dict index = 0
 DEFAULT_UNKNOWN_LABEL = '<unk>'  # dict index = 1
 DEFAULT_RESERVED_LABEL = ['<reserved-2>',
@@ -84,7 +88,7 @@ class BasePreprocess(object):
         return len(self.label2index)
 
     def run(self, train_dev_data, test_data=None, pickle_path="./", train_dev_split=0, cross_val=False, n_fold=10):
-        """Main preprocessing pipeline.
+        """Main pre-processing pipeline.
 
         :param train_dev_data: three-level list, with either single label or multiple labels in a sample.
         :param test_data: three-level list, with either single label or multiple labels in a sample. (optional)
@@ -92,7 +96,9 @@ class BasePreprocess(object):
         :param train_dev_split: float, between [0, 1]. The ratio of training data used as validation set.
         :param cross_val: bool, whether to do cross validation.
         :param n_fold: int, the number of folds of cross validation. Only useful when cross_val is True.
-        :return results: a tuple of datasets after preprocessing.
+        :return results: multiple datasets after pre-processing. If test_data is provided, return one more dataset.
+                If train_dev_split > 0, return one more dataset - the dev set. If cross_val is True, each dataset
+                is a list of DataSet objects; Otherwise, each dataset is a DataSet object.
         """
 
         if pickle_exist(pickle_path, "word2id.pkl") and pickle_exist(pickle_path, "class2id.pkl"):
@@ -111,68 +117,87 @@ class BasePreprocess(object):
             index2label = self.build_reverse_dict(self.label2index)
             save_pickle(index2label, pickle_path, "id2class.pkl")
 
-        data_train = []
-        data_dev = []
+        train_set = []
+        dev_set = []
         if not cross_val:
             if not pickle_exist(pickle_path, "data_train.pkl"):
-                data_train.extend(self.to_index(train_dev_data))
                 if train_dev_split > 0 and not pickle_exist(pickle_path, "data_dev.pkl"):
-                    split = int(len(data_train) * train_dev_split)
-                    data_dev = data_train[: split]
-                    data_train = data_train[split:]
-                    save_pickle(data_dev, pickle_path, "data_dev.pkl")
+                    split = int(len(train_dev_data) * train_dev_split)
+                    data_dev = train_dev_data[: split]
+                    data_train = train_dev_data[split:]
+                    train_set = self.convert_to_dataset(data_train, self.word2index, self.label2index)
+                    dev_set = self.convert_to_dataset(data_dev, self.word2index, self.label2index)
+
+                    save_pickle(dev_set, pickle_path, "data_dev.pkl")
                     print("{} of the training data is split for validation. ".format(train_dev_split))
-                save_pickle(data_train, pickle_path, "data_train.pkl")
+                else:
+                    train_set = self.convert_to_dataset(train_dev_data, self.word2index, self.label2index)
+                save_pickle(train_set, pickle_path, "data_train.pkl")
             else:
-                data_train = load_pickle(pickle_path, "data_train.pkl")
+                train_set = load_pickle(pickle_path, "data_train.pkl")
                 if pickle_exist(pickle_path, "data_dev.pkl"):
-                    data_dev = load_pickle(pickle_path, "data_dev.pkl")
+                    dev_set = load_pickle(pickle_path, "data_dev.pkl")
         else:
             # cross_val is True
             if not pickle_exist(pickle_path, "data_train_0.pkl"):
                 # cross validation
-                data_idx = self.to_index(train_dev_data)
-                data_cv = self.cv_split(data_idx, n_fold)
+                data_cv = self.cv_split(train_dev_data, n_fold)
                 for i, (data_train_cv, data_dev_cv) in enumerate(data_cv):
+                    data_train_cv = self.convert_to_dataset(data_train_cv, self.word2index, self.label2index)
+                    data_dev_cv = self.convert_to_dataset(data_dev_cv, self.word2index, self.label2index)
                     save_pickle(
                         data_train_cv, pickle_path,
                         "data_train_{}.pkl".format(i))
                     save_pickle(
                         data_dev_cv, pickle_path,
                         "data_dev_{}.pkl".format(i))
-                    data_train.append(data_train_cv)
-                    data_dev.append(data_dev_cv)
+                    train_set.append(data_train_cv)
+                    dev_set.append(data_dev_cv)
                 print("{}-fold cross validation.".format(n_fold))
             else:
                 for i in range(n_fold):
                     data_train_cv = load_pickle(pickle_path, "data_train_{}.pkl".format(i))
                     data_dev_cv = load_pickle(pickle_path, "data_dev_{}.pkl".format(i))
-                    data_train.append(data_train_cv)
-                    data_dev.append(data_dev_cv)
+                    train_set.append(data_train_cv)
+                    dev_set.append(data_dev_cv)
 
         # prepare test data if provided
-        data_test = []
+        test_set = []
         if test_data is not None:
             if not pickle_exist(pickle_path, "data_test.pkl"):
-                data_test = self.to_index(test_data)
-                save_pickle(data_test, pickle_path, "data_test.pkl")
+                test_set = self.convert_to_dataset(test_data, self.word2index, self.label2index)
+                save_pickle(test_set, pickle_path, "data_test.pkl")
 
         # return preprocessed results
-        results = [data_train]
+        results = [train_set]
         if cross_val or train_dev_split > 0:
-            results.append(data_dev)
+            results.append(dev_set)
         if test_data:
-            results.append(data_test)
+            results.append(test_set)
         if len(results) == 1:
             return results[0]
         else:
             return tuple(results)
 
     def build_dict(self, data):
-        raise NotImplementedError
+        label2index = DEFAULT_WORD_TO_INDEX.copy()
+        word2index = DEFAULT_WORD_TO_INDEX.copy()
+        for example in data:
+            for word in example[0]:
+                if word not in word2index:
+                    word2index[word] = len(word2index)
+            label = example[1]
+            if isinstance(label, str):
+                # label is a string
+                if label not in label2index:
+                    label2index[label] = len(label2index)
+            elif isinstance(label, list):
+                # label is a list of strings
+                for single_label in label:
+                    if single_label not in label2index:
+                        label2index[single_label] = len(label2index)
+        return word2index, label2index
 
-    def to_index(self, data):
-        raise NotImplementedError
 
     def build_reverse_dict(self, word_dict):
         id2word = {word_dict[w]: w for w in word_dict}
@@ -186,11 +211,23 @@ class BasePreprocess(object):
         return data_train, data_dev
 
     def cv_split(self, data, n_fold):
-        """Split data for cross validation."""
+        """Split data for cross validation.
+
+        :param data: list of string
+        :param n_fold: int
+        :return data_cv:
+
+            ::
+            [
+                (data_train, data_dev),  # 1st fold
+                (data_train, data_dev),  # 2nd fold
+                ...
+            ]
+
+        """
         data_copy = data.copy()
         np.random.shuffle(data_copy)
         fold_size = round(len(data_copy) / n_fold)
-
         data_cv = []
         for i in range(n_fold - 1):
             start = i * fold_size
@@ -202,154 +239,72 @@ class BasePreprocess(object):
         data_dev = data_copy[start:]
         data_train = data_copy[:start]
         data_cv.append((data_train, data_dev))
-
         return data_cv
 
+    def convert_to_dataset(self, data, vocab, label_vocab):
+        """Convert list of indices into a DataSet object.
+
+        :param data: list. Entries are strings.
+        :param vocab: a dict, mapping string (token) to index (int).
+        :param label_vocab: a dict, mapping string (label) to index (int).
+        :return data_set: a DataSet object
+        """
+        use_word_seq = False
+        use_label_seq = False
+        use_label_str = False
+
+        # construct a DataSet object and fill it with Instances
+        data_set = DataSet()
+        for example in data:
+            words, label = example[0], example[1]
+            instance = Instance()
+
+            if isinstance(words, list):
+                x = TextField(words, is_target=False)
+                instance.add_field("word_seq", x)
+                use_word_seq = True
+            else:
+                raise NotImplementedError("words is a {}".format(type(words)))
+
+            if isinstance(label, list):
+                y = TextField(label, is_target=True)
+                instance.add_field("label_seq", y)
+                use_label_seq = True
+            elif isinstance(label, str):
+                y = LabelField(label, is_target=True)
+                instance.add_field("label", y)
+                use_label_str = True
+            else:
+                raise NotImplementedError("label is a {}".format(type(label)))
+            data_set.append(instance)
+
+        # convert strings to indices
+        if use_word_seq:
+            data_set.index_field("word_seq", vocab)
+        if use_label_seq:
+            data_set.index_field("label_seq", label_vocab)
+        if use_label_str:
+            data_set.index_field("label", label_vocab)
+
+        return data_set
+
 
 class SeqLabelPreprocess(BasePreprocess):
-    """Preprocess pipeline, including building mapping from words to index, from index to words,
-        from labels/classes to index, from index to labels/classes.
-        data of three-level list which have multiple labels in each sample.
-        ::
-
-            [
-                [ [word_11, word_12, ...], [label_1, label_1, ...] ],
-                [ [word_21, word_22, ...], [label_2, label_1, ...] ],
-                ...
-            ]
-
-    """
-
     def __init__(self):
+
         super(SeqLabelPreprocess, self).__init__()
 
-    def build_dict(self, data):
-        """Add new words with indices into self.word_dict, new labels with indices into self.label_dict.
-
-        :param data: three-level list
-            ::
-
-            [
-                [ [word_11, word_12, ...], [label_1, label_1, ...] ],
-                [ [word_21, word_22, ...], [label_2, label_1, ...] ],
-                ...
-            ]
-
-        :return word2index: dict of {str, int}
-                label2index: dict of {str, int}
-        """
-        # In seq labeling, both word seq and label seq need to be padded to the same length in a mini-batch.
-        label2index = DEFAULT_WORD_TO_INDEX.copy()
-        word2index = DEFAULT_WORD_TO_INDEX.copy()
-        for example in data:
-            for word, label in zip(example[0], example[1]):
-                if word not in word2index:
-                    word2index[word] = len(word2index)
-                if label not in label2index:
-                    label2index[label] = len(label2index)
-        return word2index, label2index
-
-    def to_index(self, data):
-        """Convert word strings and label strings into indices.
-
-        :param data: three-level list
-            ::
-
-            [
-                [ [word_11, word_12, ...], [label_1, label_1, ...] ],
-                [ [word_21, word_22, ...], [label_2, label_1, ...] ],
-                ...
-            ]
-
-        :return data_index: the same shape as data, but each string is replaced by its corresponding index
-        """
-        data_index = []
-        for example in data:
-            word_list = []
-            label_list = []
-            for word, label in zip(example[0], example[1]):
-                word_list.append(self.word2index.get(word, DEFAULT_WORD_TO_INDEX[DEFAULT_UNKNOWN_LABEL]))
-                label_list.append(self.label2index.get(label, DEFAULT_WORD_TO_INDEX[DEFAULT_UNKNOWN_LABEL]))
-            data_index.append([word_list, label_list])
-        return data_index
 
 
 class ClassPreprocess(BasePreprocess):
-    """ Preprocess pipeline for classification datasets.
-        Preprocess pipeline, including building mapping from words to index, from index to words,
-        from labels/classes to index, from index to labels/classes.
-        design for data of three-level list which has a single label in each sample.
-            ::
-
-            [
-                [ [word_11, word_12, ...], label_1 ],
-                [ [word_21, word_22, ...], label_2 ],
-                ...
-            ]
-
-    """
-
     def __init__(self):
         super(ClassPreprocess, self).__init__()
 
-    def build_dict(self, data):
-        """Build vocabulary."""
 
-        # build vocabulary from scratch if nothing exists
-        word2index = DEFAULT_WORD_TO_INDEX.copy()
-        label2index = {} # DEFAULT_WORD_TO_INDEX.copy()
-
-        # collect every word and label
-        for sent, label in data:
-            if len(sent) <= 1:
-                continue
-
-            if label not in label2index:
-                label2index[label] = len(label2index)
-
-            for word in sent:
-                if word not in word2index:
-                    word2index[word] = len(word2index)
-        return word2index, label2index
-
-    def to_index(self, data):
-        """Convert word strings and label strings into indices.
-
-        :param data: three-level list
-        ::
-
-            [
-                [ [word_11, word_12, ...], label_1 ],
-                [ [word_21, word_22, ...], label_2 ],
-                ...
-            ]
-
-        :return data_index: the same shape as data, but each string is replaced by its corresponding index
-        """
-        data_index = []
-        for example in data:
-            word_list = []
-            # example[0] is the word list, example[1] is the single label
-            for word in example[0]:
-                word_list.append(self.word2index.get(word, DEFAULT_WORD_TO_INDEX[DEFAULT_UNKNOWN_LABEL]))
-            label_index = self.label2index.get(example[1], DEFAULT_WORD_TO_INDEX[DEFAULT_UNKNOWN_LABEL])
-            data_index.append([word_list, label_index])
-        return data_index
-
-
-def infer_preprocess(pickle_path, data):
-    """Preprocess over inference data. Transform three-level list of strings into that of index.
-        ::
-
-        [
-            [word_11, word_12, ...],
-            [word_21, word_22, ...],
-            ...
-        ]
-
-    """
-    word2index = load_pickle(pickle_path, "word2id.pkl")
-    data_index = []
-    for example in data:
-        data_index.append([word2index.get(w, DEFAULT_UNKNOWN_LABEL) for w in example])
-    return data_index
+if __name__ == "__main__":
+    p = BasePreprocess()
+    train_dev_data = [[["I", "am", "a", "good", "student", "."], "0"],
+                      [["You", "are", "pretty", "."], "1"]
+                      ]
+    training_set = p.run(train_dev_data)
+    print(training_set)
diff --git a/fastNLP/core/tester.py b/fastNLP/core/tester.py
index bcb6ba8c..aaa96283 100644
--- a/fastNLP/core/tester.py
+++ b/fastNLP/core/tester.py
@@ -1,9 +1,8 @@
 import numpy as np
 import torch
 
-from fastNLP.core.action import Action
-from fastNLP.core.action import RandomSampler, Batchifier
-from fastNLP.modules import utils
+from fastNLP.core.action import RandomSampler
+from fastNLP.core.batch import Batch
 from fastNLP.saver.logger import create_logger
 
 logger = create_logger(__name__, "./train_test.log")
@@ -35,16 +34,16 @@ class BaseTester(object):
         """
             "required_args" is the collection of arguments that users must pass to Trainer explicitly. 
             This is used to warn users of essential settings in the training. 
-            Obviously, "required_args" is the subset of "default_args". 
-            The value in "default_args" to the keys in "required_args" is simply for type check. 
+            Specially, "required_args" does not have default value, so they have nothing to do with "default_args".
         """
-        # add required arguments here
-        required_args = {}
+        required_args = {"task"  # one of ("seq_label", "text_classify")
+                         }
 
         for req_key in required_args:
             if req_key not in kwargs:
                 logger.error("Tester lacks argument {}".format(req_key))
                 raise ValueError("Tester lacks argument {}".format(req_key))
+        self._task = kwargs["task"]
 
         for key in default_args:
             if key in kwargs:
@@ -79,14 +78,14 @@ class BaseTester(object):
             self._model = network
 
         # turn on the testing mode; clean up the history
-        self.mode(network, test=True)
+        self.mode(network, is_test=True)
         self.eval_history.clear()
         self.batch_output.clear()
 
-        iterator = iter(Batchifier(RandomSampler(dev_data), self.batch_size, drop_last=False))
+        data_iterator = Batch(dev_data, self.batch_size, sampler=RandomSampler(), use_cuda=self.use_cuda)
         step = 0
 
-        for batch_x, batch_y in self.make_batch(iterator):
+        for batch_x, batch_y in data_iterator:
             with torch.no_grad():
                 prediction = self.data_forward(network, batch_x)
                 eval_results = self.evaluate(prediction, batch_y)
@@ -102,17 +101,22 @@ class BaseTester(object):
                 print(self.make_eval_output(prediction, eval_results))
             step += 1
 
-    def mode(self, model, test):
+    def mode(self, model, is_test=False):
         """Train mode or Test mode. This is for PyTorch currently.
 
         :param model: a PyTorch model
-        :param test: bool, whether in test mode.
+        :param is_test: bool, whether in test mode or not.
+
         """
-        Action.mode(model, test)
+        if is_test:
+            model.eval()
+        else:
+            model.train()
 
     def data_forward(self, network, x):
         """A forward pass of the model. """
-        raise NotImplementedError
+        y = network(**x)
+        return y
 
     def evaluate(self, predict, truth):
         """Compute evaluation metrics.
@@ -121,7 +125,38 @@ class BaseTester(object):
         :param truth: Tensor
         :return eval_results: can be anything. It will be stored in self.eval_history
         """
-        raise NotImplementedError
+        if "label_seq" in truth:
+            truth = truth["label_seq"]
+        elif "label" in truth:
+            truth = truth["label"]
+        else:
+            raise NotImplementedError("Unknown key {} in batch_y.".format(truth.keys()))
+
+        if self._task == "seq_label":
+            return self._seq_label_evaluate(predict, truth)
+        elif self._task == "text_classify":
+            return self._text_classify_evaluate(predict, truth)
+        else:
+            raise NotImplementedError("Unknown task type {}.".format(self._task))
+
+    def _seq_label_evaluate(self, predict, truth):
+        batch_size, max_len = predict.size(0), predict.size(1)
+        loss = self._model.loss(predict, truth) / batch_size
+        prediction = self._model.prediction(predict)
+        # pad prediction to equal length
+        for pred in prediction:
+            if len(pred) < max_len:
+                pred += [0] * (max_len - len(pred))
+        results = torch.Tensor(prediction).view(-1, )
+
+        # make sure "results" is in the same device as "truth"
+        results = results.to(truth)
+        accuracy = torch.sum(results == truth.view((-1,))).to(torch.float) / results.shape[0]
+        return [float(loss), float(accuracy)]
+
+    def _text_classify_evaluate(self, y_logit, y_true):
+        y_prob = torch.nn.functional.softmax(y_logit, dim=-1)
+        return [y_prob, y_true]
 
     @property
     def metrics(self):
@@ -131,7 +166,27 @@ class BaseTester(object):
 
         :return : variable number of outputs
         """
-        raise NotImplementedError
+        if self._task == "seq_label":
+            return self._seq_label_metrics
+        elif self._task == "text_classify":
+            return self._text_classify_metrics
+        else:
+            raise NotImplementedError("Unknown task type {}.".format(self._task))
+
+    @property
+    def _seq_label_metrics(self):
+        batch_loss = np.mean([x[0] for x in self.eval_history])
+        batch_accuracy = np.mean([x[1] for x in self.eval_history])
+        return batch_loss, batch_accuracy
+
+    @property
+    def _text_classify_metrics(self):
+        y_prob, y_true = zip(*self.eval_history)
+        y_prob = torch.cat(y_prob, dim=0)
+        y_pred = torch.argmax(y_prob, dim=-1)
+        y_true = torch.cat(y_true, dim=0)
+        acc = float(torch.sum(y_pred == y_true)) / len(y_true)
+        return y_true.cpu().numpy(), y_prob.cpu().numpy(), acc
 
     def show_metrics(self):
         """Customize evaluation outputs in Trainer.
@@ -140,10 +195,8 @@ class BaseTester(object):
 
         :return print_str: str
         """
-        raise NotImplementedError
-
-    def make_batch(self, iterator):
-        raise NotImplementedError
+        loss, accuracy = self.metrics
+        return "dev loss={:.2f}, accuracy={:.2f}".format(loss, accuracy)
 
     def make_eval_output(self, predictions, eval_results):
         """Customize Tester outputs.
@@ -152,108 +205,20 @@ class BaseTester(object):
         :param eval_results: Tensor
         :return: str, to be printed.
         """
-        raise NotImplementedError
+        return self.show_metrics()
+
 
 class SeqLabelTester(BaseTester):
-    """Tester for sequence labeling.
-
-    """
-
     def __init__(self, **test_args):
-        """
-        :param test_args: a dict-like object that has __getitem__ method, can be accessed by "test_args["key_str"]"
-        """
+        test_args.update({"task": "seq_label"})
+        print(
+            "[FastNLP Warning] SeqLabelTester will be deprecated. Please use Tester with argument 'task'='seq_label'.")
         super(SeqLabelTester, self).__init__(**test_args)
-        self.max_len = None
-        self.mask = None
-        self.seq_len = None
-
-    def data_forward(self, network, inputs):
-        """This is only for sequence labeling with CRF decoder.
-
-        :param network: a PyTorch model
-        :param inputs: tuple of (x, seq_len)
-                        x: Tensor of shape [batch_size, max_len], where max_len is the maximum length of the mini-batch
-                            after padding.
-                        seq_len: list of int, the lengths of sequences before padding.
-        :return y: Tensor of shape [batch_size, max_len]
-        """
-        if not isinstance(inputs, tuple):
-            raise RuntimeError("output_length must be true for sequence modeling.")
-        # unpack the returned value from make_batch
-        x, seq_len = inputs[0], inputs[1]
-        batch_size, max_len = x.size(0), x.size(1)
-        mask = utils.seq_mask(seq_len, max_len)
-        mask = mask.byte().view(batch_size, max_len)
-        if torch.cuda.is_available() and self.use_cuda:
-            mask = mask.cuda()
-        self.mask = mask
-        self.seq_len = seq_len
-        y = network(x)
-        return y
-
-    def evaluate(self, predict, truth):
-        """Compute metrics (or loss).
-
-        :param predict: Tensor, [batch_size, max_len, tag_size]
-        :param truth: Tensor, [batch_size, max_len]
-        :return:
-        """
-        batch_size, max_len = predict.size(0), predict.size(1)
-        loss = self._model.loss(predict, truth, self.mask) / batch_size
-
-        prediction = self._model.prediction(predict, self.mask)
-        results = torch.Tensor(prediction).view(-1, )
-        # make sure "results" is in the same device as "truth"
-        results = results.to(truth)
-        accuracy = torch.sum(results == truth.view((-1,))).to(torch.float) / results.shape[0]
-        return [float(loss), float(accuracy)]
-
-    def metrics(self):
-        batch_loss = np.mean([x[0] for x in self.eval_history])
-        batch_accuracy = np.mean([x[1] for x in self.eval_history])
-        return batch_loss, batch_accuracy
-
-    def show_metrics(self):
-        """This is called by Trainer to print evaluation on dev set.
-
-        :return print_str: str
-        """
-        loss, accuracy = self.metrics()
-        return "dev loss={:.2f}, accuracy={:.2f}".format(loss, accuracy)
-
-    def make_batch(self, iterator):
-        return Action.make_batch(iterator, use_cuda=self.use_cuda, output_length=True)
 
 
 class ClassificationTester(BaseTester):
-    """Tester for classification."""
-
     def __init__(self, **test_args):
-        """
-        :param test_args: a dict-like object that has __getitem__ method.
-            can be accessed by "test_args["key_str"]"
-        """
+        test_args.update({"task": "seq_label"})
+        print(
+            "[FastNLP Warning] ClassificationTester will be deprecated. Please use Tester with argument 'task'='text_classify'.")
         super(ClassificationTester, self).__init__(**test_args)
-
-    def make_batch(self, iterator, max_len=None):
-        return Action.make_batch(iterator, use_cuda=self.use_cuda, max_len=max_len)
-
-    def data_forward(self, network, x):
-        """Forward through network."""
-        logits = network(x)
-        return logits
-
-    def evaluate(self, y_logit, y_true):
-        """Return y_pred and y_true."""
-        y_prob = torch.nn.functional.softmax(y_logit, dim=-1)
-        return [y_prob, y_true]
-
-    def metrics(self):
-        """Compute accuracy."""
-        y_prob, y_true = zip(*self.eval_history)
-        y_prob = torch.cat(y_prob, dim=0)
-        y_pred = torch.argmax(y_prob, dim=-1)
-        y_true = torch.cat(y_true, dim=0)
-        acc = float(torch.sum(y_pred == y_true)) / len(y_true)
-        return y_true.cpu().numpy(), y_prob.cpu().numpy(), acc
diff --git a/fastNLP/core/trainer.py b/fastNLP/core/trainer.py
index 523a1763..e638fdde 100644
--- a/fastNLP/core/trainer.py
+++ b/fastNLP/core/trainer.py
@@ -4,15 +4,13 @@ import time
 from datetime import timedelta
 
 import torch
-import tensorboardX
 from tensorboardX import SummaryWriter
 
-from fastNLP.core.action import Action
-from fastNLP.core.action import RandomSampler, Batchifier
+from fastNLP.core.action import RandomSampler
+from fastNLP.core.batch import Batch
 from fastNLP.core.loss import Loss
 from fastNLP.core.optimizer import Optimizer
 from fastNLP.core.tester import SeqLabelTester, ClassificationTester
-from fastNLP.modules import utils
 from fastNLP.saver.logger import create_logger
 from fastNLP.saver.model_saver import ModelSaver
 
@@ -50,16 +48,16 @@ class BaseTrainer(object):
         """
             "required_args" is the collection of arguments that users must pass to Trainer explicitly. 
             This is used to warn users of essential settings in the training. 
-            Obviously, "required_args" is the subset of "default_args". 
-            The value in "default_args" to the keys in "required_args" is simply for type check. 
+            Specially, "required_args" does not have default value, so they have nothing to do with "default_args".
         """
-        # add required arguments here
-        required_args = {}
+        required_args = {"task"  # one of ("seq_label", "text_classify")
+                         }
 
         for req_key in required_args:
             if req_key not in kwargs:
                 logger.error("Trainer lacks argument {}".format(req_key))
                 raise ValueError("Trainer lacks argument {}".format(req_key))
+        self._task = kwargs["task"]
 
         for key in default_args:
             if key in kwargs:
@@ -90,13 +88,14 @@ class BaseTrainer(object):
         self._optimizer_proto = default_args["optimizer"]
         self._summary_writer = SummaryWriter(self.pickle_path + 'tensorboard_logs')
         self._graph_summaried = False
+        self._best_accuracy = 0.0
 
     def train(self, network, train_data, dev_data=None):
         """General Training Procedure
 
         :param network: a model
-        :param train_data: three-level list, the training set.
-        :param dev_data: three-level list, the validation data (optional)
+        :param train_data: a DataSet instance, the training data
+        :param dev_data: a DataSet instance, the validation data (optional)
         """
         # transfer model to gpu if available
         if torch.cuda.is_available() and self.use_cuda:
@@ -126,9 +125,10 @@ class BaseTrainer(object):
             logger.info("training epoch {}".format(epoch))
 
             # turn on network training mode
-            self.mode(network, test=False)
+            self.mode(network, is_test=False)
             # prepare mini-batch iterator
-            data_iterator = iter(Batchifier(RandomSampler(train_data), self.batch_size, drop_last=False))
+            data_iterator = Batch(train_data, batch_size=self.batch_size, sampler=RandomSampler(),
+                                  use_cuda=self.use_cuda)
             logger.info("prepared data iterator")
 
             # one forward and backward pass
@@ -157,7 +157,7 @@ class BaseTrainer(object):
                 - epoch: int,
         """
         step = 0
-        for batch_x, batch_y in self.make_batch(data_iterator):
+        for batch_x, batch_y in data_iterator:
 
             prediction = self.data_forward(network, batch_x)
 
@@ -166,10 +166,6 @@ class BaseTrainer(object):
             self.update()
             self._summary_writer.add_scalar("loss", loss.item(), global_step=step)
 
-            if not self._graph_summaried:
-                self._summary_writer.add_graph(network, batch_x)
-                self._graph_summaried = True
-
             if kwargs["n_print"] > 0 and step % kwargs["n_print"] == 0:
                 end = time.time()
                 diff = timedelta(seconds=round(end - kwargs["start"]))
@@ -204,11 +200,17 @@ class BaseTrainer(object):
             network_copy = copy.deepcopy(network)
             self.train(network_copy, train_data_cv[i], dev_data_cv[i])
 
-    def make_batch(self, iterator):
-        raise NotImplementedError
+    def mode(self, model, is_test=False):
+        """Train mode or Test mode. This is for PyTorch currently.
 
-    def mode(self, network, test):
-        Action.mode(network, test)
+        :param model: a PyTorch model
+        :param is_test: bool, whether in test mode or not.
+
+        """
+        if is_test:
+            model.eval()
+        else:
+            model.train()
 
     def define_optimizer(self):
         """Define framework-specific optimizer specified by the models.
@@ -224,7 +226,20 @@ class BaseTrainer(object):
         self._optimizer.step()
 
     def data_forward(self, network, x):
-        raise NotImplementedError
+        if self._task == "seq_label":
+            y = network(x["word_seq"], x["word_seq_origin_len"])
+        elif self._task == "text_classify":
+            y = network(x["word_seq"])
+        else:
+            raise NotImplementedError("Unknown task type {}.".format(self._task))
+
+        if not self._graph_summaried:
+            if self._task == "seq_label":
+                self._summary_writer.add_graph(network, (x["word_seq"], x["word_seq_origin_len"]), verbose=False)
+            elif self._task == "text_classify":
+                self._summary_writer.add_graph(network, x["word_seq"], verbose=False)
+            self._graph_summaried = True
+        return y
 
     def grad_backward(self, loss):
         """Compute gradient with link rules.
@@ -243,6 +258,13 @@ class BaseTrainer(object):
         :param truth: ground truth label vector
         :return: a scalar
         """
+        if "label_seq" in truth:
+            truth = truth["label_seq"]
+        elif "label" in truth:
+            truth = truth["label"]
+            truth = truth.view((-1,))
+        else:
+            raise NotImplementedError("Unknown key {} in batch_y.".format(truth.keys()))
         return self._loss_func(predict, truth)
 
     def define_loss(self):
@@ -270,7 +292,12 @@ class BaseTrainer(object):
         :param validator: a Tester instance
         :return: bool, True means current results on dev set is the best.
         """
-        raise NotImplementedError
+        loss, accuracy = validator.metrics
+        if accuracy > self._best_accuracy:
+            self._best_accuracy = accuracy
+            return True
+        else:
+            return False
 
     def save_model(self, network, model_name):
         """Save this model with such a name.
@@ -291,55 +318,11 @@ class SeqLabelTrainer(BaseTrainer):
     """Trainer for Sequence Labeling
 
     """
-
     def __init__(self, **kwargs):
+        kwargs.update({"task": "seq_label"})
+        print(
+            "[FastNLP Warning] SeqLabelTrainer will be deprecated. Please use Trainer with argument 'task'='seq_label'.")
         super(SeqLabelTrainer, self).__init__(**kwargs)
-        # self.vocab_size = kwargs["vocab_size"]
-        # self.num_classes = kwargs["num_classes"]
-        self.max_len = None
-        self.mask = None
-        self.best_accuracy = 0.0
-
-    def data_forward(self, network, inputs):
-        if not isinstance(inputs, tuple):
-            raise RuntimeError("output_length must be true for sequence modeling. Receive {}".format(type(inputs[0])))
-        # unpack the returned value from make_batch
-        x, seq_len = inputs[0], inputs[1]
-
-        batch_size, max_len = x.size(0), x.size(1)
-        mask = utils.seq_mask(seq_len, max_len)
-        mask = mask.byte().view(batch_size, max_len)
-
-        if torch.cuda.is_available() and self.use_cuda:
-            mask = mask.cuda()
-        self.mask = mask
-
-        y = network(x)
-        return y
-
-    def get_loss(self, predict, truth):
-        """Compute loss given prediction and ground truth.
-
-        :param predict: prediction label vector, [batch_size, max_len, tag_size]
-        :param truth: ground truth label vector, [batch_size, max_len]
-        :return loss: a scalar
-        """
-        batch_size, max_len = predict.size(0), predict.size(1)
-        assert truth.shape == (batch_size, max_len)
-
-        loss = self._model.loss(predict, truth, self.mask)
-        return loss
-
-    def best_eval_result(self, validator):
-        loss, accuracy = validator.metrics()
-        if accuracy > self.best_accuracy:
-            self.best_accuracy = accuracy
-            return True
-        else:
-            return False
-
-    def make_batch(self, iterator):
-        return Action.make_batch(iterator, output_length=True, use_cuda=self.use_cuda)
 
     def _create_validator(self, valid_args):
         return SeqLabelTester(**valid_args)
@@ -349,33 +332,10 @@ class ClassificationTrainer(BaseTrainer):
     """Trainer for text classification."""
 
     def __init__(self, **train_args):
+        train_args.update({"task": "text_classify"})
+        print(
+            "[FastNLP Warning] ClassificationTrainer will be deprecated. Please use Trainer with argument 'task'='text_classify'.")
         super(ClassificationTrainer, self).__init__(**train_args)
 
-        self.iterator = None
-        self.loss_func = None
-        self.optimizer = None
-        self.best_accuracy = 0
-
-    def data_forward(self, network, x):
-        """Forward through network."""
-        logits = network(x)
-        return logits
-
-    def make_batch(self, iterator):
-        return Action.make_batch(iterator, output_length=False, use_cuda=self.use_cuda)
-
-    def get_acc(self, y_logit, y_true):
-        """Compute accuracy."""
-        y_pred = torch.argmax(y_logit, dim=-1)
-        return int(torch.sum(y_true == y_pred)) / len(y_true)
-
-    def best_eval_result(self, validator):
-        _, _, accuracy = validator.metrics()
-        if accuracy > self.best_accuracy:
-            self.best_accuracy = accuracy
-            return True
-        else:
-            return False
-
     def _create_validator(self, valid_args):
         return ClassificationTester(**valid_args)
diff --git a/fastNLP/models/cnn_text_classification.py b/fastNLP/models/cnn_text_classification.py
index fc7388a5..15a65221 100644
--- a/fastNLP/models/cnn_text_classification.py
+++ b/fastNLP/models/cnn_text_classification.py
@@ -35,8 +35,12 @@ class CNNText(torch.nn.Module):
         self.dropout = nn.Dropout(drop_prob)
         self.fc = encoder.linear.Linear(sum(kernel_nums), num_classes)
 
-    def forward(self, x):
-        x = self.embed(x)  # [N,L] -> [N,L,C]
+    def forward(self, word_seq):
+        """
+        :param word_seq: torch.LongTensor, [batch_size, seq_len]
+        :return x: torch.LongTensor, [batch_size, num_classes]
+        """
+        x = self.embed(word_seq)  # [N,L] -> [N,L,C]
         x = self.conv_pool(x)  # [N,L,C] -> [N,C]
         x = self.dropout(x)
         x = self.fc(x)  # [N,C] -> [N, N_class]
diff --git a/fastNLP/models/sequence_modeling.py b/fastNLP/models/sequence_modeling.py
index 5addc73e..c2bcc693 100644
--- a/fastNLP/models/sequence_modeling.py
+++ b/fastNLP/models/sequence_modeling.py
@@ -4,6 +4,20 @@ from fastNLP.models.base_model import BaseModel
 from fastNLP.modules import decoder, encoder
 
 
+def seq_mask(seq_len, max_len):
+    """Create a mask for the sequences.
+
+    :param seq_len: list or torch.LongTensor
+    :param max_len: int
+    :return mask: torch.LongTensor
+    """
+    if isinstance(seq_len, list):
+        seq_len = torch.LongTensor(seq_len)
+    mask = [torch.ge(seq_len, i + 1) for i in range(max_len)]
+    mask = torch.stack(mask, 1)
+    return mask
+
+
 class SeqLabeling(BaseModel):
     """
     PyTorch Network for sequence labeling
@@ -20,13 +34,17 @@ class SeqLabeling(BaseModel):
         self.Rnn = encoder.lstm.Lstm(word_emb_dim, hidden_dim)
         self.Linear = encoder.linear.Linear(hidden_dim, num_classes)
         self.Crf = decoder.CRF.ConditionalRandomField(num_classes)
+        self.mask = None
 
-    def forward(self, x):
+    def forward(self, word_seq, word_seq_origin_len):
         """
-        :param x: LongTensor, [batch_size, mex_len]
+        :param word_seq: LongTensor, [batch_size, mex_len]
+        :param word_seq_origin_len: LongTensor, [batch_size,], the origin lengths of the sequences.
         :return y: [batch_size, mex_len, tag_size]
         """
-        x = self.Embedding(x)
+        self.mask = self.make_mask(word_seq, word_seq_origin_len)
+
+        x = self.Embedding(word_seq)
         # [batch_size, max_len, word_emb_dim]
         x = self.Rnn(x)
         # [batch_size, max_len, hidden_size * direction]
@@ -34,27 +52,34 @@ class SeqLabeling(BaseModel):
         # [batch_size, max_len, num_classes]
         return x
 
-    def loss(self, x, y, mask):
+    def loss(self, x, y):
         """
         Negative log likelihood loss.
         :param x: Tensor, [batch_size, max_len, tag_size]
         :param y: Tensor, [batch_size, max_len]
-        :param mask: ByteTensor, [batch_size, ,max_len]
         :return loss: a scalar Tensor
 
         """
         x = x.float()
         y = y.long()
-        total_loss = self.Crf(x, y, mask)
+        assert x.shape[:2] == y.shape
+        assert y.shape == self.mask.shape
+        total_loss = self.Crf(x, y, self.mask)
         return torch.mean(total_loss)
 
-    def prediction(self, x, mask):
+    def make_mask(self, x, seq_len):
+        batch_size, max_len = x.size(0), x.size(1)
+        mask = seq_mask(seq_len, max_len)
+        mask = mask.byte().view(batch_size, max_len)
+        mask = mask.to(x)
+        return mask
+
+    def prediction(self, x):
         """
         :param x: FloatTensor, [batch_size, max_len, tag_size]
-        :param mask: ByteTensor, [batch_size, max_len]
         :return prediction: list of [decode path(list)]
         """
-        tag_seq = self.Crf.viterbi_decode(x, mask)
+        tag_seq = self.Crf.viterbi_decode(x, self.mask)
         return tag_seq
 
 
@@ -81,14 +106,17 @@ class AdvSeqLabel(SeqLabeling):
 
         self.Crf = decoder.CRF.ConditionalRandomField(num_classes)
 
-    def forward(self, x):
+    def forward(self, word_seq, word_seq_origin_len):
         """
-        :param x: LongTensor, [batch_size, mex_len]
+        :param word_seq: LongTensor, [batch_size, mex_len]
+        :param word_seq_origin_len: list of int.
         :return y: [batch_size, mex_len, tag_size]
         """
-        batch_size = x.size(0)
-        max_len = x.size(1)
-        x = self.Embedding(x)
+        self.mask = self.make_mask(word_seq, word_seq_origin_len)
+
+        batch_size = word_seq.size(0)
+        max_len = word_seq.size(1)
+        x = self.Embedding(word_seq)
         # [batch_size, max_len, word_emb_dim]
         x = self.Rnn(x)
         # [batch_size, max_len, hidden_size * direction]
diff --git a/test/core/test_action.py b/test/core/test_action.py
deleted file mode 100644
index 8d0f628b..00000000
--- a/test/core/test_action.py
+++ /dev/null
@@ -1,17 +0,0 @@
-import unittest
-
-from fastNLP.core.action import Action, Batchifier, SequentialSampler
-
-
-class TestAction(unittest.TestCase):
-    def test_case_1(self):
-        x = [1, 2, 3, 4, 5, 6, 7, 8]
-        y = [1, 1, 1, 1, 2, 2, 2, 2]
-        data = []
-        for i in range(len(x)):
-            data.append([[x[i]], [y[i]]])
-        data = Batchifier(SequentialSampler(data), batch_size=2, drop_last=False)
-        action = Action()
-        for batch_x in action.make_batch(data, use_cuda=False, output_length=True, max_len=None):
-            print(batch_x)
-
diff --git a/test/core/test_batch.py b/test/core/test_batch.py
new file mode 100644
index 00000000..395aeb2b
--- /dev/null
+++ b/test/core/test_batch.py
@@ -0,0 +1,62 @@
+import unittest
+
+import torch
+
+from fastNLP.core.batch import Batch
+from fastNLP.core.dataset import DataSet, create_dataset_from_lists
+from fastNLP.core.field import TextField, LabelField
+from fastNLP.core.instance import Instance
+
+raw_texts = ["i am a cat",
+             "this is a test of new batch",
+             "ha ha",
+             "I am a good boy .",
+             "This is the most beautiful girl ."
+             ]
+texts = [text.strip().split() for text in raw_texts]
+labels = [0, 1, 0, 0, 1]
+
+# prepare vocabulary
+vocab = {}
+for text in texts:
+    for tokens in text:
+        if tokens not in vocab:
+            vocab[tokens] = len(vocab)
+
+
+class TestCase1(unittest.TestCase):
+    def test(self):
+        data = DataSet()
+        for text, label in zip(texts, labels):
+            x = TextField(text, is_target=False)
+            y = LabelField(label, is_target=True)
+            ins = Instance(text=x, label=y)
+            data.append(ins)
+
+        # use vocabulary to index data
+        data.index_field("text", vocab)
+
+        # define naive sampler for batch class
+        class SeqSampler:
+            def __call__(self, dataset):
+                return list(range(len(dataset)))
+
+        # use batch to iterate dataset
+        data_iterator = Batch(data, 2, SeqSampler(), False)
+        for batch_x, batch_y in data_iterator:
+            self.assertEqual(len(batch_x), 2)
+            self.assertTrue(isinstance(batch_x, dict))
+            self.assertTrue(isinstance(batch_x["text"], torch.LongTensor))
+            self.assertTrue(isinstance(batch_y, dict))
+            self.assertTrue(isinstance(batch_y["label"], torch.LongTensor))
+
+
+class TestCase2(unittest.TestCase):
+    def test(self):
+        data = DataSet()
+        for text in texts:
+            x = TextField(text, is_target=False)
+            ins = Instance(text=x)
+            data.append(ins)
+        data_set = create_dataset_from_lists(texts, vocab, has_target=False)
+        self.assertTrue(type(data) == type(data_set))
diff --git a/test/core/test_predictor.py b/test/core/test_predictor.py
new file mode 100644
index 00000000..c7ad65d7
--- /dev/null
+++ b/test/core/test_predictor.py
@@ -0,0 +1,51 @@
+import os
+import unittest
+
+from fastNLP.core.predictor import Predictor
+from fastNLP.core.preprocess import save_pickle
+from fastNLP.models.sequence_modeling import SeqLabeling
+
+
+class TestPredictor(unittest.TestCase):
+    def test_seq_label(self):
+        model_args = {
+            "vocab_size": 10,
+            "word_emb_dim": 100,
+            "rnn_hidden_units": 100,
+            "num_classes": 5
+        }
+
+        infer_data = [
+            ['a', 'b', 'c', 'd', 'e'],
+            ['a', '@', 'c', 'd', 'e'],
+            ['a', 'b', '#', 'd', 'e'],
+            ['a', 'b', 'c', '?', 'e'],
+            ['a', 'b', 'c', 'd', '$'],
+            ['!', 'b', 'c', 'd', 'e']
+        ]
+        vocab = {'a': 0, 'b': 1, 'c': 2, 'd': 3, 'e': 4, '!': 5, '@': 6, '#': 7, '$': 8, '?': 9}
+
+        os.system("mkdir save")
+        save_pickle({0: "0", 1: "1", 2: "2", 3: "3", 4: "4"}, "./save/", "id2class.pkl")
+        save_pickle(vocab, "./save/", "word2id.pkl")
+
+        model = SeqLabeling(model_args)
+        predictor = Predictor("./save/", task="seq_label")
+
+        results = predictor.predict(network=model, data=infer_data)
+
+        self.assertTrue(isinstance(results, list))
+        self.assertGreater(len(results), 0)
+        for res in results:
+            self.assertTrue(isinstance(res, list))
+            self.assertEqual(len(res), 5)
+            self.assertTrue(isinstance(res[0], str))
+
+        os.system("rm -rf save")
+        print("pickle path deleted")
+
+
+class TestPredictor2(unittest.TestCase):
+    def test_text_classify(self):
+        # TODO
+        pass
diff --git a/test/core/test_preprocess.py b/test/core/test_preprocess.py
index bff33ed3..05c04ce9 100644
--- a/test/core/test_preprocess.py
+++ b/test/core/test_preprocess.py
@@ -1,24 +1,25 @@
 import os
 import unittest
 
+from fastNLP.core.dataset import DataSet
 from fastNLP.core.preprocess import SeqLabelPreprocess
 
+data = [
+    [['Tom', 'and', 'Jerry', '.'], ['n', '&', 'n', '.']],
+    [['Hello', 'world', '!'], ['a', 'n', '.']],
+    [['Tom', 'and', 'Jerry', '.'], ['n', '&', 'n', '.']],
+    [['Hello', 'world', '!'], ['a', 'n', '.']],
+    [['Tom', 'and', 'Jerry', '.'], ['n', '&', 'n', '.']],
+    [['Hello', 'world', '!'], ['a', 'n', '.']],
+    [['Tom', 'and', 'Jerry', '.'], ['n', '&', 'n', '.']],
+    [['Hello', 'world', '!'], ['a', 'n', '.']],
+    [['Tom', 'and', 'Jerry', '.'], ['n', '&', 'n', '.']],
+    [['Hello', 'world', '!'], ['a', 'n', '.']],
+]
 
-class TestSeqLabelPreprocess(unittest.TestCase):
-    def test_case_1(self):
-        data = [
-            [['Tom', 'and', 'Jerry', '.'], ['n', '&', 'n', '.']],
-            [['Hello', 'world', '!'], ['a', 'n', '.']],
-            [['Tom', 'and', 'Jerry', '.'], ['n', '&', 'n', '.']],
-            [['Hello', 'world', '!'], ['a', 'n', '.']],
-            [['Tom', 'and', 'Jerry', '.'], ['n', '&', 'n', '.']],
-            [['Hello', 'world', '!'], ['a', 'n', '.']],
-            [['Tom', 'and', 'Jerry', '.'], ['n', '&', 'n', '.']],
-            [['Hello', 'world', '!'], ['a', 'n', '.']],
-            [['Tom', 'and', 'Jerry', '.'], ['n', '&', 'n', '.']],
-            [['Hello', 'world', '!'], ['a', 'n', '.']],
-        ]
 
+class TestCase1(unittest.TestCase):
+    def test(self):
         if os.path.exists("./save"):
             for root, dirs, files in os.walk("./save", topdown=False):
                 for name in files:
@@ -27,17 +28,45 @@ class TestSeqLabelPreprocess(unittest.TestCase):
                     os.rmdir(os.path.join(root, name))
         result = SeqLabelPreprocess().run(train_dev_data=data, train_dev_split=0.4,
                                           pickle_path="./save")
-        result = SeqLabelPreprocess().run(train_dev_data=data, train_dev_split=0.4,
-                                          pickle_path="./save")
+        self.assertEqual(len(result), 2)
+        self.assertEqual(type(result[0]), DataSet)
+        self.assertEqual(type(result[1]), DataSet)
+
+        os.system("rm -rf save")
+        print("pickle path deleted")
+
+
+class TestCase2(unittest.TestCase):
+    def test(self):
         if os.path.exists("./save"):
             for root, dirs, files in os.walk("./save", topdown=False):
                 for name in files:
                     os.remove(os.path.join(root, name))
                 for name in dirs:
                     os.rmdir(os.path.join(root, name))
-        result = SeqLabelPreprocess().run(test_data=data, train_dev_data=data,
-                                                           pickle_path="./save", train_dev_split=0.4,
-                                                           cross_val=True)
         result = SeqLabelPreprocess().run(test_data=data, train_dev_data=data,
                                           pickle_path="./save", train_dev_split=0.4,
-                                          cross_val=True)
+                                          cross_val=False)
+        self.assertEqual(len(result), 3)
+        self.assertEqual(type(result[0]), DataSet)
+        self.assertEqual(type(result[1]), DataSet)
+        self.assertEqual(type(result[2]), DataSet)
+
+        os.system("rm -rf save")
+        print("pickle path deleted")
+
+
+class TestCase3(unittest.TestCase):
+    def test(self):
+        num_folds = 2
+        result = SeqLabelPreprocess().run(test_data=None, train_dev_data=data,
+                                          pickle_path="./save", train_dev_split=0.4,
+                                          cross_val=True, n_fold=num_folds)
+        self.assertEqual(len(result), 2)
+        self.assertEqual(len(result[0]), num_folds)
+        self.assertEqual(len(result[1]), num_folds)
+        for data_set in result[0] + result[1]:
+            self.assertEqual(type(data_set), DataSet)
+
+        os.system("rm -rf save")
+        print("pickle path deleted")
diff --git a/test/core/test_tester.py b/test/core/test_tester.py
index e4ccf536..aa277b9a 100644
--- a/test/core/test_tester.py
+++ b/test/core/test_tester.py
@@ -1,37 +1,55 @@
-from fastNLP.core.preprocess import SeqLabelPreprocess
+import os
+import unittest
+
+from fastNLP.core.dataset import DataSet
+from fastNLP.core.field import TextField
+from fastNLP.core.instance import Instance
 from fastNLP.core.tester import SeqLabelTester
-from fastNLP.loader.config_loader import ConfigSection, ConfigLoader
-from fastNLP.loader.dataset_loader import TokenizeDatasetLoader
 from fastNLP.models.sequence_modeling import SeqLabeling
 
 data_name = "pku_training.utf8"
 pickle_path = "data_for_tests"
 
 
-def foo():
-    loader = TokenizeDatasetLoader("./data_for_tests/cws_pku_utf_8")
-    train_data = loader.load_pku()
+class TestTester(unittest.TestCase):
+    def test_case_1(self):
+        model_args = {
+            "vocab_size": 10,
+            "word_emb_dim": 100,
+            "rnn_hidden_units": 100,
+            "num_classes": 5
+        }
+        valid_args = {"save_output": True, "validate_in_training": True, "save_dev_input": True,
+                      "save_loss": True, "batch_size": 2, "pickle_path": "./save/",
+                      "use_cuda": False, "print_every_step": 1}
 
-    train_args = ConfigSection()
-    ConfigLoader("config.cfg").load_config("./data_for_tests/config", {"POS": train_args})
+        train_data = [
+            [['a', 'b', 'c', 'd', 'e'], ['a', '@', 'c', 'd', 'e']],
+            [['a', '@', 'c', 'd', 'e'], ['a', '@', 'c', 'd', 'e']],
+            [['a', 'b', '#', 'd', 'e'], ['a', '@', 'c', 'd', 'e']],
+            [['a', 'b', 'c', '?', 'e'], ['a', '@', 'c', 'd', 'e']],
+            [['a', 'b', 'c', 'd', '$'], ['a', '@', 'c', 'd', 'e']],
+            [['!', 'b', 'c', 'd', 'e'], ['a', '@', 'c', 'd', 'e']],
+        ]
+        vocab = {'a': 0, 'b': 1, 'c': 2, 'd': 3, 'e': 4, '!': 5, '@': 6, '#': 7, '$': 8, '?': 9}
+        label_vocab = {'a': 0, '@': 1, 'c': 2, 'd': 3, 'e': 4}
 
-    # Preprocessor
-    p = SeqLabelPreprocess()
-    train_data = p.run(train_data)
-    train_args["vocab_size"] = p.vocab_size
-    train_args["num_classes"] = p.num_classes
+        data_set = DataSet()
+        for example in train_data:
+            text, label = example[0], example[1]
+            x = TextField(text, False)
+            y = TextField(label, is_target=True)
+            ins = Instance(word_seq=x, label_seq=y)
+            data_set.append(ins)
 
-    model = SeqLabeling(train_args)
+        data_set.index_field("word_seq", vocab)
+        data_set.index_field("label_seq", label_vocab)
 
-    valid_args = {"save_output": True, "validate_in_training": True, "save_dev_input": True,
-                  "save_loss": True, "batch_size": 8, "pickle_path": "./data_for_tests/",
-                  "use_cuda": True}
-    validator = SeqLabelTester(**valid_args)
+        model = SeqLabeling(model_args)
 
-    print("start validation.")
-    validator.test(model, train_data)
-    print(validator.show_metrics())
+        tester = SeqLabelTester(**valid_args)
+        tester.test(network=model, dev_data=data_set)
+        # If this can run, everything is OK.
 
-
-if __name__ == "__main__":
-    foo()
+        os.system("rm -rf save")
+        print("pickle path deleted")
diff --git a/test/core/test_trainer.py b/test/core/test_trainer.py
index 7db861af..c71cd695 100644
--- a/test/core/test_trainer.py
+++ b/test/core/test_trainer.py
@@ -1,33 +1,54 @@
 import os
-
-import torch.nn as nn
 import unittest
 
-from fastNLP.core.trainer import SeqLabelTrainer
+from fastNLP.core.dataset import DataSet
+from fastNLP.core.field import TextField
+from fastNLP.core.instance import Instance
 from fastNLP.core.loss import Loss
 from fastNLP.core.optimizer import Optimizer
+from fastNLP.core.trainer import SeqLabelTrainer
 from fastNLP.models.sequence_modeling import SeqLabeling
 
+
 class TestTrainer(unittest.TestCase):
     def test_case_1(self):
-        args = {"epochs": 3, "batch_size": 8, "validate": True, "use_cuda": True, "pickle_path": "./save/",
+        args = {"epochs": 3, "batch_size": 2, "validate": True, "use_cuda": False, "pickle_path": "./save/",
                 "save_best_dev": True, "model_name": "default_model_name.pkl",
                 "loss": Loss(None),
                 "optimizer": Optimizer("Adam", lr=0.001, weight_decay=0),
-                "vocab_size": 20,
+                "vocab_size": 10,
                 "word_emb_dim": 100,
                 "rnn_hidden_units": 100,
-                "num_classes": 3
+                "num_classes": 5
                 }
-        trainer = SeqLabelTrainer()
+        trainer = SeqLabelTrainer(**args)
+
         train_data = [
-            [[1, 2, 3, 4, 5, 6], [1, 0, 1, 0, 1, 2]],
-            [[2, 3, 4, 5, 1, 6], [0, 1, 0, 1, 0, 2]],
-            [[1, 4, 1, 4, 1, 6], [1, 0, 1, 0, 1, 2]],
-            [[1, 2, 3, 4, 5, 6], [1, 0, 1, 0, 1, 2]],
-            [[2, 3, 4, 5, 1, 6], [0, 1, 0, 1, 0, 2]],
-            [[1, 4, 1, 4, 1, 6], [1, 0, 1, 0, 1, 2]],
+            [['a', 'b', 'c', 'd', 'e'], ['a', '@', 'c', 'd', 'e']],
+            [['a', '@', 'c', 'd', 'e'], ['a', '@', 'c', 'd', 'e']],
+            [['a', 'b', '#', 'd', 'e'], ['a', '@', 'c', 'd', 'e']],
+            [['a', 'b', 'c', '?', 'e'], ['a', '@', 'c', 'd', 'e']],
+            [['a', 'b', 'c', 'd', '$'], ['a', '@', 'c', 'd', 'e']],
+            [['!', 'b', 'c', 'd', 'e'], ['a', '@', 'c', 'd', 'e']],
         ]
-        dev_data = train_data
+        vocab = {'a': 0, 'b': 1, 'c': 2, 'd': 3, 'e': 4, '!': 5, '@': 6, '#': 7, '$': 8, '?': 9}
+        label_vocab = {'a': 0, '@': 1, 'c': 2, 'd': 3, 'e': 4}
+
+        data_set = DataSet()
+        for example in train_data:
+            text, label = example[0], example[1]
+            x = TextField(text, False)
+            y = TextField(label, is_target=True)
+            ins = Instance(word_seq=x, label_seq=y)
+            data_set.append(ins)
+
+        data_set.index_field("word_seq", vocab)
+        data_set.index_field("label_seq", label_vocab)
+
         model = SeqLabeling(args)
-        trainer.train(network=model, train_data=train_data, dev_data=dev_data)
\ No newline at end of file
+
+        trainer.train(network=model, train_data=data_set, dev_data=data_set)
+        # If this can run, everything is OK.
+
+        os.system("rm -rf save")
+        print("pickle path deleted")
diff --git a/test/model/seq_labeling.py b/test/model/seq_labeling.py
index 0f7a072b..d7750b17 100644
--- a/test/model/seq_labeling.py
+++ b/test/model/seq_labeling.py
@@ -15,11 +15,11 @@ from fastNLP.core.optimizer import Optimizer
 
 parser = argparse.ArgumentParser()
 parser.add_argument("-s", "--save", type=str, default="./seq_label/", help="path to save pickle files")
-parser.add_argument("-t", "--train", type=str, default="./data_for_tests/people.txt",
+parser.add_argument("-t", "--train", type=str, default="../data_for_tests/people.txt",
                     help="path to the training data")
-parser.add_argument("-c", "--config", type=str, default="./data_for_tests/config", help="path to the config file")
+parser.add_argument("-c", "--config", type=str, default="../data_for_tests/config", help="path to the config file")
 parser.add_argument("-m", "--model_name", type=str, default="seq_label_model.pkl", help="the name of the model")
-parser.add_argument("-i", "--infer", type=str, default="data_for_tests/people_infer.txt",
+parser.add_argument("-i", "--infer", type=str, default="../data_for_tests/people_infer.txt",
                     help="data used for inference")
 
 args = parser.parse_args()
@@ -86,7 +86,7 @@ def train_and_test():
     trainer = SeqLabelTrainer(
         epochs=trainer_args["epochs"],
         batch_size=trainer_args["batch_size"],
-        validate=trainer_args["validate"],
+        validate=False,
         use_cuda=trainer_args["use_cuda"],
         pickle_path=pickle_path,
         save_best_dev=trainer_args["save_best_dev"],
@@ -121,7 +121,7 @@ def train_and_test():
 
     # Tester
     tester = SeqLabelTester(save_output=False,
-                            save_loss=False,
+                            save_loss=True,
                             save_best_dev=False,
                             batch_size=4,
                             use_cuda=False,
@@ -139,5 +139,5 @@ def train_and_test():
 
 
 if __name__ == "__main__":
-    # train_and_test()
-    infer()
+    train_and_test()
+    # infer()
diff --git a/test/model/test_charlm.py b/test/model/test_charlm.py
deleted file mode 100644
index e76f6404..00000000
--- a/test/model/test_charlm.py
+++ /dev/null
@@ -1,8 +0,0 @@
-
-
-def test_charlm():
-    pass
-
-
-if __name__ == "__main__":
-    test_charlm()
diff --git a/test/model/test_seq_label.py b/test/model/test_seq_label.py
new file mode 100644
index 00000000..c4ca5476
--- /dev/null
+++ b/test/model/test_seq_label.py
@@ -0,0 +1,85 @@
+import os
+
+from fastNLP.core.optimizer import Optimizer
+from fastNLP.core.preprocess import SeqLabelPreprocess
+from fastNLP.core.tester import SeqLabelTester
+from fastNLP.core.trainer import SeqLabelTrainer
+from fastNLP.loader.config_loader import ConfigLoader, ConfigSection
+from fastNLP.loader.dataset_loader import POSDatasetLoader
+from fastNLP.loader.model_loader import ModelLoader
+from fastNLP.models.sequence_modeling import SeqLabeling
+from fastNLP.saver.model_saver import ModelSaver
+
+pickle_path = "./seq_label/"
+model_name = "seq_label_model.pkl"
+config_dir = "test/data_for_tests/config"
+data_path = "test/data_for_tests/people.txt"
+data_infer_path = "test/data_for_tests/people_infer.txt"
+
+
+def test_training():
+    # Config Loader
+    trainer_args = ConfigSection()
+    model_args = ConfigSection()
+    ConfigLoader("_").load_config(config_dir, {
+        "test_seq_label_trainer": trainer_args, "test_seq_label_model": model_args})
+
+    # Data Loader
+    pos_loader = POSDatasetLoader(data_path)
+    train_data = pos_loader.load_lines()
+
+    # Preprocessor
+    p = SeqLabelPreprocess()
+    data_train, data_dev = p.run(train_data, pickle_path=pickle_path, train_dev_split=0.5)
+    model_args["vocab_size"] = p.vocab_size
+    model_args["num_classes"] = p.num_classes
+
+    trainer = SeqLabelTrainer(
+        epochs=trainer_args["epochs"],
+        batch_size=trainer_args["batch_size"],
+        validate=False,
+        use_cuda=False,
+        pickle_path=pickle_path,
+        save_best_dev=trainer_args["save_best_dev"],
+        model_name=model_name,
+        optimizer=Optimizer("SGD", lr=0.01, momentum=0.9),
+    )
+
+    # Model
+    model = SeqLabeling(model_args)
+
+    # Start training
+    trainer.train(model, data_train, data_dev)
+
+    # Saver
+    saver = ModelSaver(os.path.join(pickle_path, model_name))
+    saver.save_pytorch(model)
+
+    del model, trainer, pos_loader
+
+    # Define the same model
+    model = SeqLabeling(model_args)
+
+    # Dump trained parameters into the model
+    ModelLoader.load_pytorch(model, os.path.join(pickle_path, model_name))
+
+    # Load test configuration
+    tester_args = ConfigSection()
+    ConfigLoader("config.cfg").load_config(config_dir, {"test_seq_label_tester": tester_args})
+
+    # Tester
+    tester = SeqLabelTester(save_output=False,
+                            save_loss=True,
+                            save_best_dev=False,
+                            batch_size=4,
+                            use_cuda=False,
+                            pickle_path=pickle_path,
+                            model_name="seq_label_in_test.pkl",
+                            print_every_step=1
+                            )
+
+    # Start testing with validation data
+    tester.test(model, data_dev)
+
+    loss, accuracy = tester.metrics
+    assert 0 < accuracy < 1
diff --git a/test/model/text_classify.py b/test/model/text_classify.py
index 6ff3c059..381a768e 100644
--- a/test/model/text_classify.py
+++ b/test/model/text_classify.py
@@ -19,9 +19,9 @@ from fastNLP.core.loss import Loss
 
 parser = argparse.ArgumentParser()
 parser.add_argument("-s", "--save", type=str, default="./test_classification/", help="path to save pickle files")
-parser.add_argument("-t", "--train", type=str, default="./data_for_tests/text_classify.txt",
+parser.add_argument("-t", "--train", type=str, default="../data_for_tests/text_classify.txt",
                     help="path to the training data")
-parser.add_argument("-c", "--config", type=str, default="./data_for_tests/config", help="path to the config file")
+parser.add_argument("-c", "--config", type=str, default="../data_for_tests/config", help="path to the config file")
 parser.add_argument("-m", "--model_name", type=str, default="classify_model.pkl", help="the name of the model")
 
 args = parser.parse_args()
@@ -115,4 +115,4 @@ def train():
 
 if __name__ == "__main__":
     train()
-    infer()
+    # infer()