diff --git a/src/client/src/tscSQLParser.c b/src/client/src/tscSQLParser.c
index 7adc0812ae12bd8711cba5988806a4c7ba740cf5..573933388699d14ee039f19054830a2e105c126b 100644
--- a/src/client/src/tscSQLParser.c
+++ b/src/client/src/tscSQLParser.c
@@ -5884,6 +5884,11 @@ int32_t setAlterTableInfo(SSqlObj* pSql, struct SSqlInfo* pInfo) {
 
     tVariantListItem* pItem = taosArrayGet(pVarList, 1);
     SSchema* pTagsSchema = tscGetTableColumnSchema(pTableMetaInfo->pTableMeta, columnIndex.columnIndex);
+
+    if (IS_VAR_DATA_TYPE(pTagsSchema->type) && (pItem->pVar.nLen > pTagsSchema->bytes * TSDB_NCHAR_SIZE)) {
+      return invalidOperationMsg(pMsg, msg14);
+    }
+
     pAlterSQL->tagData.data = calloc(1, pTagsSchema->bytes * TSDB_NCHAR_SIZE + VARSTR_HEADER_SIZE);
 
     if (tVariantDump(&pItem->pVar, pAlterSQL->tagData.data, pTagsSchema->type, true) != TSDB_CODE_SUCCESS) {
diff --git a/tests/pytest/tag_lite/TestModifyTag.py b/tests/pytest/tag_lite/TestModifyTag.py
new file mode 100644
index 0000000000000000000000000000000000000000..acf63695f6dcc52d2ae9df8cdead96802cd1f4b3
--- /dev/null
+++ b/tests/pytest/tag_lite/TestModifyTag.py
@@ -0,0 +1,125 @@
+###################################################################
+#           Copyright (c) 2016 by TAOS Technologies, Inc.
+#                     All rights reserved.
+#
+#  This file is proprietary and confidential to TAOS Technologies.
+#  No part of this file may be reproduced, stored, transmitted,
+#  disclosed or used in any form or by any means other than as
+#  expressly provided by the written permission from Jianhui Tao
+#
+###################################################################
+
+# -*- coding: utf-8 -*-
+
+import sys
+import os
+from util.log import *
+from util.cases import *
+from util.sql import *
+from util.dnodes import *
+
+
+class TDTestCase:
+    def init(self, conn, logSql):
+        tdLog.debug("start to execute %s" % __file__)
+        tdSql.init(conn.cursor(), logSql)
+
+        self.ts = 1625068800000000000   # this is timestamp  "2021-07-01 00:00:00"
+        self.numberOfTables = 10
+        self.numberOfRecords = 100
+
+    def checkCommunity(self):
+        selfPath = os.path.dirname(os.path.realpath(__file__))
+        if ("community" in selfPath):
+            return False
+        else:
+            return True
+
+    def getBuildPath(self):
+        selfPath = os.path.dirname(os.path.realpath(__file__))
+
+        if ("community" in selfPath):
+            projPath = selfPath[:selfPath.find("community")]
+        else:
+            projPath = selfPath[:selfPath.find("tests")]
+
+        for root, dirs, files in os.walk(projPath):
+            if ("taosdump" in files):
+                rootRealPath = os.path.dirname(os.path.realpath(root))
+                if ("packaging" not in rootRealPath):
+                    buildPath = root[:len(root) - len("/build/bin")]
+                    break
+        return buildPath
+    
+    
+
+    def run(self):
+
+        buildPath = self.getBuildPath()
+        if (buildPath == ""):
+            tdLog.exit("taosdump not found!")
+        else:
+            tdLog.info("taosdump found in %s" % buildPath)
+        binPath = buildPath + "/build/bin/"
+
+        # basic test for alter tags
+        tdSql.execute("create database tagdb ")
+        tdSql.execute(" use tagdb")
+        tdSql.execute("create table st (ts timestamp , a int) tags (tg1 binary(20), tg2 binary(20), tg3 binary(20))")
+        tdSql.execute("insert into t using st (tg3, tg2, tg1) tags ('tg3', 'tg2', 'tg1') values (now, 1)")
+        tdSql.execute("alter table t set tag tg1='newtg1'")
+        res = tdSql.getResult("select tg1,tg2,tg3 from t")
+
+        if res == [('newtg1', 'tg2', 'tg3')]:
+            tdLog.info(" alter tag check has pass!")
+        else:
+            tdLog.info(" alter tag failed , please check !")
+
+        tdSql.error("alter stable st modify tag tg2 binary(2)")
+        tdSql.execute("alter stable st modify tag tg2 binary(30) ")
+        tdSql.execute("alter table t set tag tg2 = 'abcdefghijklmnopqrstuvwxyz1234'")
+        res = tdSql.getResult("select tg1,tg2,tg3 from t")
+        if res == [('newtg1', 'abcdefghijklmnopqrstuvwxyz1234', 'tg3')]:
+            tdLog.info(" alter tag check has pass!")
+        else:
+            tdLog.info(" alter tag failed , please check !")
+
+        # test boundary about tags
+        tdSql.execute("create stable stb1 (ts timestamp , a int) tags (tg1 binary(16374))")
+        tdSql.error("create stable stb1 (ts timestamp , a int) tags (tg1 binary(16375))")
+        bound_sql = "create stable stb2 (ts timestamp , a int) tags (tg1 binary(10),"
+        for i in range(127):
+            bound_sql+="tag"+str(i)+" binary(10),"
+        sql1 = bound_sql[:-1]+")"
+        tdSql.execute(sql1)
+        sql2 = bound_sql[:-1]+"tag127 binary(10))"
+        tdSql.error(sql2)
+        tdSql.execute("create stable stb3 (ts timestamp , a int) tags (tg1 nchar(4093))")
+        tdSql.error("create stable stb3 (ts timestamp , a int) tags (tg1 nchar(4094))")
+        tdSql.execute("create stable stb4 (ts timestamp , a int) tags (tg1 nchar(4093),tag2 binary(8))")
+        tdSql.error("create stable stb4 (ts timestamp , a int) tags (tg1 nchar(4093),tag2 binary(9))")
+        tdSql.execute("create stable stb5 (ts timestamp , a int) tags (tg1 nchar(4093),tag2 binary(4),tag3 binary(2))")
+        tdSql.error("create stable stb5 (ts timestamp , a int) tags (tg1 nchar(4093),tag2 binary(4),tag3 binary(3))")
+
+        tdSql.execute("create table stt (ts timestamp , a binary(100)) tags (tg1 binary(20), tg2 binary(20), tg3 binary(20))")
+        tdSql.execute("insert into tt using stt (tg3, tg2, tg1) tags ('tg3', 'tg2', 'tg1') values (now, 1)")
+        tags = "t"*16337
+        sql3 = "alter table tt set tag tg1=" +"'"+tags+"'"
+        tdSql.error(sql3)
+        tdSql.execute("alter stable stt modify tag tg1 binary(16337)")
+        tdSql.execute(sql3)
+        res = tdSql.getResult("select tg1,tg2,tg3 from tt")
+        if res == [(tags, 'tg2', 'tg3')]:
+            tdLog.info(" alter tag check has pass!")
+        else:
+            tdLog.info(" alter tag failed , please check !")
+        
+        os.system("rm -rf ./tag_lite/TestModifyTag.py.sql")
+
+    def stop(self):
+        tdSql.close()
+        tdLog.success("%s successfully executed" % __file__)
+
+
+tdCases.addWindows(__file__, TDTestCase())
+tdCases.addLinux(__file__, TDTestCase())
\ No newline at end of file