diff --git a/src/client/inc/tscUtil.h b/src/client/inc/tscUtil.h
index e380dc77768a97a267ce80f8fb20273acb389fa7..f7d3aa630f24e0054a1ce963e6a1939a511fe4d7 100644
--- a/src/client/inc/tscUtil.h
+++ b/src/client/inc/tscUtil.h
@@ -400,7 +400,7 @@ void tscRemoveCachedTableMeta(STableMetaInfo* pTableMetaInfo, uint64_t id);
 
 char* cloneCurrentDBName(SSqlObj* pSql);
 
-int parseJsontoTagData(char* json, SKVRowBuilder* kvRowBuilder, char* errMsg, int16_t startColId);
+int parseJsontoTagData(char* json, uint32_t jsonLength, SKVRowBuilder* kvRowBuilder, char* errMsg, int16_t startColId);
 int8_t jsonType2DbType(double data, int jsonType);
 void getJsonKey(SStrToken *t0);
 
diff --git a/src/client/src/tscParseInsert.c b/src/client/src/tscParseInsert.c
index c5719dde276abecd667efc95a960ab1a45af6962..af8c6837219cc32e22491427f04a19f70a8e50b0 100644
--- a/src/client/src/tscParseInsert.c
+++ b/src/client/src/tscParseInsert.c
@@ -1068,7 +1068,7 @@ static int32_t tscCheckIfCreateTable(char **sqlstr, SSqlObj *pSql, char** boundC
           tfree(tmp);
           return tscSQLSyntaxErrMsg(pInsertParam->msg, "json tag too long", NULL);
         }
-        code = parseJsontoTagData(sToken.z, &kvRowBuilder, pInsertParam->msg, pTagSchema[spd.boundedColumns[0]].colId);
+        code = parseJsontoTagData(sToken.z, sToken.n, &kvRowBuilder, pInsertParam->msg, pTagSchema[spd.boundedColumns[0]].colId);
         if (code != TSDB_CODE_SUCCESS) {
           tdDestroyKVRowBuilder(&kvRowBuilder);
           tscDestroyBoundColumnInfo(&spd);
diff --git a/src/client/src/tscSQLParser.c b/src/client/src/tscSQLParser.c
index 2ab7e93c388e4e195f1c961f8a43089b0fc5aa65..6cb419335fec21e564a98d8bcb7b363946e17af6 100644
--- a/src/client/src/tscSQLParser.c
+++ b/src/client/src/tscSQLParser.c
@@ -7364,7 +7364,7 @@ int32_t setAlterTableInfo(SSqlObj* pSql, struct SSqlInfo* pInfo) {
       int8_t tagVal = TSDB_DATA_JSON_PLACEHOLDER;
       tdAddColToKVRow(&kvRowBuilder, pTagsSchema->colId, pTagsSchema->type, &tagVal, false);
 
-      code = parseJsontoTagData(pItem->pVar.pz, &kvRowBuilder, pMsg, pTagsSchema->colId);
+      code = parseJsontoTagData(pItem->pVar.pz, pItem->pVar.nLen, &kvRowBuilder, pMsg, pTagsSchema->colId);
       if (code != TSDB_CODE_SUCCESS) {
         tdDestroyKVRowBuilder(&kvRowBuilder);
         return code;
@@ -9170,7 +9170,7 @@ int32_t doCheckForCreateFromStable(SSqlObj* pSql, SSqlInfo* pInfo) {
         return invalidOperationMsg(tscGetErrorMsgPayload(pCmd), msg3);
       }
 
-      ret = parseJsontoTagData(pItem->pVar.pz, &kvRowBuilder, tscGetErrorMsgPayload(pCmd), pTagSchema[0].colId);
+      ret = parseJsontoTagData(pItem->pVar.pz, pItem->pVar.nLen, &kvRowBuilder, tscGetErrorMsgPayload(pCmd), pTagSchema[0].colId);
       if (ret != TSDB_CODE_SUCCESS) {
         tdDestroyKVRowBuilder(&kvRowBuilder);
         return ret;
diff --git a/src/client/src/tscUtil.c b/src/client/src/tscUtil.c
index ee676cfa021ae841c8b55d3bc80aa3e66d9da1d7..dff3f3212835fc15d7fb976bc0f960c9e4446ad9 100644
--- a/src/client/src/tscUtil.c
+++ b/src/client/src/tscUtil.c
@@ -5393,7 +5393,7 @@ char* cloneCurrentDBName(SSqlObj* pSql) {
   return p;
 }
 
-int parseJsontoTagData(char* json, SKVRowBuilder* kvRowBuilder, char* errMsg, int16_t startColId){
+int parseJsontoTagData(char* json, uint32_t jsonLength, SKVRowBuilder* kvRowBuilder, char* errMsg, int16_t startColId){
   // set json NULL data
   uint8_t nullTypeVal[CHAR_BYTES + VARSTR_HEADER_SIZE + INT_BYTES] = {0};
   uint32_t jsonNULL = TSDB_DATA_JSON_NULL;
@@ -5404,7 +5404,7 @@ int parseJsontoTagData(char* json, SKVRowBuilder* kvRowBuilder, char* errMsg, in
   varDataSetLen(nullTypeVal + CHAR_BYTES, INT_BYTES);
   *(uint32_t*)(varDataVal(nullTypeKey)) = jsonNULL;
   tdAddColToKVRow(kvRowBuilder, jsonIndex++, TSDB_DATA_TYPE_NCHAR, nullTypeKey, false);   // add json null type
-  if (!json || strtrim(json) == 0 || strncasecmp(json, "null", 4) == 0){
+  if (!json || strtrim(json) == 0 || (jsonLength == strlen("null") && strncasecmp(json, "null", 4) == 0)){
     *(uint32_t*)(varDataVal(nullTypeVal + CHAR_BYTES)) = jsonNULL;
     tdAddColToKVRow(kvRowBuilder, jsonIndex++, TSDB_DATA_TYPE_NCHAR, nullTypeVal, true);   // add json null value
     return TSDB_CODE_SUCCESS;
diff --git a/tests/develop-test/0-others/json_tag.py b/tests/develop-test/0-others/json_tag.py
index d3891a796a675da54d7180dadd2621b5ec7caae9..c78e48b6d19bc1b977db417233b6e12c61a66112 100644
--- a/tests/develop-test/0-others/json_tag.py
+++ b/tests/develop-test/0-others/json_tag.py
@@ -530,6 +530,26 @@ class TDTestCase:
         tdSql.checkData(5, 2, 4096)
         tdSql.query("describe jsons1_1")
         tdSql.checkData(5, 2, 4096)
+        
+        #test TD-13918
+        tdSql.execute("drop table  if exists jsons_13918_1")
+        tdSql.execute("drop table  if exists jsons_13918_2")
+        tdSql.execute("drop table  if exists jsons_13918_3")
+        tdSql.execute("drop table  if exists jsons_13918_4")
+        tdSql.execute("drop table  if exists jsons_stb")
+        tdSql.execute("create table jsons_stb (ts timestamp, dataInt int) tags (jtag json)")
+        tdSql.error("create table jsons_13918_1 using jsons_stb tags ('nullx')")
+        tdSql.error("create table jsons_13918_2 using jsons_stb tags (nullx)")
+        tdSql.error("insert into jsons_13918_3 using jsons_stb tags('NULLx') values(1591061628001, 11)")
+        tdSql.error("insert into jsons_13918_4 using jsons_stb tags(NULLx) values(1591061628002, 11)")
+        tdSql.execute("create table jsons_13918_1 using jsons_stb tags ('null')")
+        tdSql.execute("create table jsons_13918_2 using jsons_stb tags (null)")
+        tdSql.execute("insert into jsons_13918_1 values(1591061628003, 11)")
+        tdSql.execute("insert into jsons_13918_2 values(1591061628004, 11)")
+        tdSql.execute("insert into jsons_13918_3 using jsons_stb tags('NULL') values(1591061628005, 11)")
+        tdSql.execute("insert into jsons_13918_4 using jsons_stb tags(\"NULL\") values(1591061628006, 11)")
+        tdSql.query("select * from jsons_stb")
+        tdSql.checkRows(4)
 
     def stop(self):
         tdSql.close()