diff --git a/dolphinscheduler-api/src/main/java/org/apache/dolphinscheduler/api/service/impl/UsersServiceImpl.java b/dolphinscheduler-api/src/main/java/org/apache/dolphinscheduler/api/service/impl/UsersServiceImpl.java
index ac6b38adcc..cfe6fb4e9f 100644
--- a/dolphinscheduler-api/src/main/java/org/apache/dolphinscheduler/api/service/impl/UsersServiceImpl.java
+++ b/dolphinscheduler-api/src/main/java/org/apache/dolphinscheduler/api/service/impl/UsersServiceImpl.java
@@ -73,6 +73,7 @@ import java.util.List;
 import java.util.Map;
 import java.util.Set;
 import java.util.TimeZone;
+import java.util.Arrays;
 import java.util.stream.Collectors;
 
 /**
@@ -526,7 +527,6 @@ public class UsersServiceImpl extends BaseServiceImpl implements UsersService {
         userMapper.queryTenantCodeByUserId(id);
 
 
-
         accessTokenMapper.deleteAccessTokenByUserId(id);
 
         userMapper.deleteById(id);
@@ -562,10 +562,7 @@ public class UsersServiceImpl extends BaseServiceImpl implements UsersService {
         if (check(result, StringUtils.isEmpty(projectIds), Status.SUCCESS)) {
             return result;
         }
-
-        String[] projectIdArr = projectIds.split(",");
-
-        for (String projectId : projectIdArr) {
+        Arrays.stream(projectIds.split(",")).distinct().forEach(projectId -> {
             Date now = new Date();
             ProjectUser projectUser = new ProjectUser();
             projectUser.setUserId(userId);
@@ -574,8 +571,7 @@ public class UsersServiceImpl extends BaseServiceImpl implements UsersService {
             projectUser.setCreateTime(now);
             projectUser.setUpdateTime(now);
             projectUserMapper.insert(projectUser);
-        }
-
+        });
         putMsg(result, Status.SUCCESS);
 
         return result;
@@ -614,15 +610,18 @@ public class UsersServiceImpl extends BaseServiceImpl implements UsersService {
             return result;
         }
 
-        // 4. maintain the relationship between project and user
-        final Date today = new Date();
-        ProjectUser projectUser = new ProjectUser();
-        projectUser.setUserId(userId);
-        projectUser.setProjectId(project.getId());
-        projectUser.setPerm(7);
-        projectUser.setCreateTime(today);
-        projectUser.setUpdateTime(today);
-        this.projectUserMapper.insert(projectUser);
+        // 4. maintain the relationship between project and user if not exists
+        ProjectUser projectUser = projectUserMapper.queryProjectRelation(project.getId(), userId);
+        if (projectUser == null) {
+            Date today = new Date();
+            projectUser = new ProjectUser();
+            projectUser.setUserId(userId);
+            projectUser.setProjectId(project.getId());
+            projectUser.setPerm(7);
+            projectUser.setCreateTime(today);
+            projectUser.setUpdateTime(today);
+            this.projectUserMapper.insert(projectUser);
+        }
 
         this.putMsg(result, Status.SUCCESS);
         return result;
diff --git a/dolphinscheduler-dao/src/main/resources/sql/dolphinscheduler_h2.sql b/dolphinscheduler-dao/src/main/resources/sql/dolphinscheduler_h2.sql
index f6cfae00e0..5623b40d99 100644
--- a/dolphinscheduler-dao/src/main/resources/sql/dolphinscheduler_h2.sql
+++ b/dolphinscheduler-dao/src/main/resources/sql/dolphinscheduler_h2.sql
@@ -709,7 +709,8 @@ CREATE TABLE t_ds_relation_project_user
     perm        int(11) DEFAULT '1',
     create_time datetime DEFAULT NULL,
     update_time datetime DEFAULT NULL,
-    PRIMARY KEY (id)
+    PRIMARY KEY (id),
+    UNIQUE KEY uniq_uid_pid(user_id,project_id)
 );
 
 -- ----------------------------
diff --git a/dolphinscheduler-dao/src/main/resources/sql/dolphinscheduler_mysql.sql b/dolphinscheduler-dao/src/main/resources/sql/dolphinscheduler_mysql.sql
index 197173a1b8..40323aa75a 100644
--- a/dolphinscheduler-dao/src/main/resources/sql/dolphinscheduler_mysql.sql
+++ b/dolphinscheduler-dao/src/main/resources/sql/dolphinscheduler_mysql.sql
@@ -709,7 +709,7 @@ CREATE TABLE `t_ds_relation_project_user` (
   `create_time` datetime DEFAULT NULL COMMENT 'create time',
   `update_time` datetime DEFAULT NULL COMMENT 'update time',
   PRIMARY KEY (`id`),
-  KEY `user_id_index` (`user_id`) USING BTREE
+  UNIQUE KEY uniq_uid_pid(user_id,project_id)
 ) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;
 
 -- ----------------------------
diff --git a/dolphinscheduler-dao/src/main/resources/sql/dolphinscheduler_postgresql.sql b/dolphinscheduler-dao/src/main/resources/sql/dolphinscheduler_postgresql.sql
index 7e5526976f..3efee9a53b 100644
--- a/dolphinscheduler-dao/src/main/resources/sql/dolphinscheduler_postgresql.sql
+++ b/dolphinscheduler-dao/src/main/resources/sql/dolphinscheduler_postgresql.sql
@@ -625,7 +625,8 @@ CREATE TABLE t_ds_relation_project_user (
   perm int DEFAULT '1' ,
   create_time timestamp DEFAULT NULL ,
   update_time timestamp DEFAULT NULL ,
-  PRIMARY KEY (id)
+  PRIMARY KEY (id),
+  CONSTRAINT t_ds_relation_project_user_un UNIQUE (user_id, project_id)
 ) ;
 create index relation_project_user_id_index on t_ds_relation_project_user (user_id);
 
diff --git a/dolphinscheduler-dao/src/main/resources/sql/upgrade/2.0.6_schema/mysql/dolphinscheduler_ddl.sql b/dolphinscheduler-dao/src/main/resources/sql/upgrade/2.0.6_schema/mysql/dolphinscheduler_ddl.sql
index 33dcab5031..b9623ad755 100644
--- a/dolphinscheduler-dao/src/main/resources/sql/upgrade/2.0.6_schema/mysql/dolphinscheduler_ddl.sql
+++ b/dolphinscheduler-dao/src/main/resources/sql/upgrade/2.0.6_schema/mysql/dolphinscheduler_ddl.sql
@@ -57,3 +57,8 @@ d//
 delimiter ;
 CALL uc_dolphin_T_t_ds_alert_R_sign;
 DROP PROCEDURE uc_dolphin_T_t_ds_alert_R_sign;
+
+-- add unique key to t_ds_relation_project_user
+ALTER TABLE t_ds_relation_project_user ADD UNIQUE KEY uniq_uid_pid(user_id,project_id);
+
+
diff --git a/dolphinscheduler-dao/src/main/resources/sql/upgrade/2.0.6_schema/postgresql/dolphinscheduler_ddl.sql b/dolphinscheduler-dao/src/main/resources/sql/upgrade/2.0.6_schema/postgresql/dolphinscheduler_ddl.sql
index 71de54fe23..9f70bf422a 100644
--- a/dolphinscheduler-dao/src/main/resources/sql/upgrade/2.0.6_schema/postgresql/dolphinscheduler_ddl.sql
+++ b/dolphinscheduler-dao/src/main/resources/sql/upgrade/2.0.6_schema/postgresql/dolphinscheduler_ddl.sql
@@ -45,4 +45,8 @@ $BODY$;
 
 select dolphin_update_metadata();
 
-d//
\ No newline at end of file
+d//
+
+-- add unique key to t_ds_relation_project_user
+CREATE UNIQUE INDEX t_ds_relation_project_user_un
+    on t_ds_relation_project_user (user_id, project_id);
\ No newline at end of file