diff --git a/fastNLP/core/trainer.py b/fastNLP/core/trainer.py
index 109315a3..add86156 100644
--- a/fastNLP/core/trainer.py
+++ b/fastNLP/core/trainer.py
@@ -51,7 +51,9 @@ class Trainer(object):
         :param Optimizer optimizer: an optimizer object
         :param int check_code_level: level of FastNLP code checker. -1: don't check, 0: ignore. 1: warning. 2: strict.\\
             `ignore` will not check unused field; `warning` when warn if some field are not used; `strict` means
-            it will raise error if some field are not used.
+            it will raise error if some field are not used. 检查的原理是通过使用很小的batch(默认两个sample)来检查代码是否能够
+            运行，但是这个过程理论上不会修改任何参数，只是会检查能否运行。但如果(1)模型中存在将batch_size写为某个固定值的情况，；(2)
+             模型中存在累加前向计算次数的，可能会多计算几次。建议将check_code_level设置为-1
         :param str metric_key: a single indicator used to decide the best model based on metric results. It must be one
             of the keys returned by the FIRST metric in `metrics`. If the overall result gets better if the indicator gets
             smaller, add "-" in front of the string. For example::
diff --git a/fastNLP/modules/aggregator/attention.py b/fastNLP/modules/aggregator/attention.py
index 3fea1b10..9f7d72dc 100644
--- a/fastNLP/modules/aggregator/attention.py
+++ b/fastNLP/modules/aggregator/attention.py
@@ -46,6 +46,21 @@ class DotAtte(nn.Module):
 
 class MultiHeadAtte(nn.Module):
     def __init__(self, input_size, output_size, key_size, value_size, num_atte):
+        """
+        实现的是以下内容
+        QW1: (batch_size, seq_len, input_size) * (input_size, key_size)
+        KW2: (batch_size, seq_len, input_size) * (input_size, key_size)
+        VW3: (batch_size, seq_len, input_size) * (input_size, value_size)
+
+        softmax(QK^T/sqrt(scale))*V: (batch_size, seq_len, value_size) 多个head(num_atten指定)的结果为
+            (batch_size, seq_len, value_size*num_atte)
+        最终结果将上式过一个（value_size*num_atte, output_size)的线性层，output为(batch_size, seq_len, output_size)
+        :param input_size: int, 输入的维度
+        :param output_size: int, 输出特征的维度
+        :param key_size: int, query和key映射到该维度
+        :param value_size: int, value映射到该维度
+        :param num_atte:
+        """
         super(MultiHeadAtte, self).__init__()
         self.in_linear = nn.ModuleList()
         for i in range(num_atte * 3):
diff --git a/reproduction/chinese_word_segment/models/cws_transformer.py b/reproduction/chinese_word_segment/models/cws_transformer.py
new file mode 100644
index 00000000..3fcf91b5
--- /dev/null
+++ b/reproduction/chinese_word_segment/models/cws_transformer.py
@@ -0,0 +1,70 @@
+
+
+
+"""
+使用transformer作为分词的encoder端
+
+"""
+
+from torch import nn
+import torch
+from fastNLP.modules.encoder.transformer import TransformerEncoder
+from fastNLP.modules.decoder.CRF import ConditionalRandomField,seq_len_to_byte_mask
+from fastNLP.modules.decoder.CRF import allowed_transitions
+
+class TransformerCWS(nn.Module):
+    def __init__(self, vocab_num, embed_dim=100, bigram_vocab_num=None, bigram_embed_dim=100, num_bigram_per_char=None,
+                 hidden_size=200, embed_drop_p=0.3, num_layers=1, num_heads=8, tag_size=4):
+        super().__init__()
+
+        self.embedding = nn.Embedding(vocab_num, embed_dim)
+        input_size = embed_dim
+        if bigram_vocab_num:
+            self.bigram_embedding = nn.Embedding(bigram_vocab_num, bigram_embed_dim)
+            input_size += num_bigram_per_char*bigram_embed_dim
+
+        self.drop = nn.Dropout(embed_drop_p, inplace=True)
+
+        self.fc1 = nn.Linear(input_size, hidden_size)
+
+        value_size = hidden_size//num_heads
+        self.transformer = TransformerEncoder(num_layers, input_size=input_size, output_size=hidden_size,
+                                              key_size=value_size, value_size=value_size, num_atte=num_heads)
+
+        self.fc2 = nn.Linear(hidden_size, tag_size)
+
+        allowed_trans = allowed_transitions({0:'b', 1:'m', 2:'e', 3:'s'}, encoding_type='bmes')
+        self.crf = ConditionalRandomField(num_tags=tag_size, include_start_end_trans=False,
+                                          allowed_transitions=allowed_trans)
+
+    def forward(self, chars, target, seq_lens, bigrams=None):
+        seq_lens = seq_lens
+        masks = seq_len_to_byte_mask(seq_lens)
+        x = self.embedding(chars)
+        batch_size = x.size(0)
+        length = x.size(1)
+        if hasattr(self, 'bigram_embedding'):
+            bigrams = self.bigram_embedding(bigrams) # batch_size x seq_lens x per_char x embed_size
+            x = torch.cat([x, bigrams.view(batch_size, length, -1)], dim=-1)
+        self.drop(x)
+        x = self.fc1(x)
+        feats = self.transformer(x, masks)
+        feats = self.fc2(feats)
+        losses = self.crf(feats, target, masks.float())
+
+        pred_dict = {}
+        pred_dict['seq_lens'] = seq_lens
+        pred_dict['loss'] = torch.mean(losses)
+
+        return pred_dict
+
+
+if __name__ == '__main__':
+    transformer = TransformerCWS(10, embed_dim=100, bigram_vocab_num=10, bigram_embed_dim=100, num_bigram_per_char=8,
+                 hidden_size=200, embed_drop_p=0.3, num_layers=1, num_heads=8, tag_size=4)
+    chars = torch.randint(10, size=(4, 7)).long()
+    bigrams = torch.randint(10, size=(4, 56)).long()
+    seq_lens = torch.ones(4).long()*7
+    target = torch.randint(4, size=(4, 7))
+
+    print(transformer(chars, target, seq_lens, bigrams))
\ No newline at end of file