diff --git a/source/libs/parser/src/parAstCreater.c b/source/libs/parser/src/parAstCreater.c
index 04ef854b5c6ecb0aa131dd452b3ce6404c744a80..e8ac5620720b59ed85f0bec546ad2f9a948a0cbe 100644
--- a/source/libs/parser/src/parAstCreater.c
+++ b/source/libs/parser/src/parAstCreater.c
@@ -363,8 +363,10 @@ SNode* createCastFunctionNode(SAstCreateContext* pCxt, SNode* pExpr, SDataType d
   CHECK_OUT_OF_MEM(func);
   strcpy(func->functionName, "cast");
   func->node.resType = dt;
-  if (TSDB_DATA_TYPE_NCHAR == dt.type) {
-    func->node.resType.bytes = func->node.resType.bytes * TSDB_NCHAR_SIZE;
+  if (TSDB_DATA_TYPE_VARCHAR == dt.type) {
+    func->node.resType.bytes = func->node.resType.bytes + VARSTR_HEADER_SIZE;
+  } else if (TSDB_DATA_TYPE_NCHAR == dt.type) {
+    func->node.resType.bytes = func->node.resType.bytes * TSDB_NCHAR_SIZE + VARSTR_HEADER_SIZE;
   }
   nodesListMakeAppend(&func->pParameterList, pExpr);
   return (SNode*)func;
diff --git a/source/libs/scalar/src/sclfunc.c b/source/libs/scalar/src/sclfunc.c
index a727d8017062eeaabdc3953c77f8b2b890221c62..0161323e37722475d64cdf2a4e4c6605eed82473 100644
--- a/source/libs/scalar/src/sclfunc.c
+++ b/source/libs/scalar/src/sclfunc.c
@@ -709,10 +709,6 @@ int32_t castFunction(SScalarParam *pInput, int32_t inputNum, SScalarParam *pOutp
   int16_t outputType = GET_PARAM_TYPE(&pOutput[0]);
   int64_t outputLen  = GET_PARAM_BYTES(&pOutput[0]);
 
-  if (IS_VAR_DATA_TYPE(outputType)) {
-    outputLen += VARSTR_HEADER_SIZE;
-  }
-
   char *outputBuf = taosMemoryCalloc(outputLen * pInput[0].numOfRows, 1);
   char *output = outputBuf;