diff --git a/source/client/src/clientEnv.c b/source/client/src/clientEnv.c
index ecfa1e3392..18907ede5d 100644
--- a/source/client/src/clientEnv.c
+++ b/source/client/src/clientEnv.c
@@ -127,7 +127,7 @@ static void generateWriteSlowLog(STscObj *pTscObj, SRequestObj *pRequest, int32_
   cJSON_AddItemToObject(json, "error_info",   cJSON_CreateString(tstrerror(pRequest->code)));
   cJSON_AddItemToObject(json, "type",         cJSON_CreateNumber(reqType));
   cJSON_AddItemToObject(json, "rows_num",     cJSON_CreateNumber(pRequest->body.resInfo.numOfRows + pRequest->body.resInfo.totalRows));
-  if(strlen(pRequest->sqlstr) > pTscObj->pAppInfo->monitorParas.tsSlowLogMaxLen){
+  if(pRequest->sqlstr != NULL && strlen(pRequest->sqlstr) > pTscObj->pAppInfo->monitorParas.tsSlowLogMaxLen){
     char tmp = pRequest->sqlstr[pTscObj->pAppInfo->monitorParas.tsSlowLogMaxLen];
     pRequest->sqlstr[pTscObj->pAppInfo->monitorParas.tsSlowLogMaxLen] = '\0';
     cJSON_AddItemToObject(json, "sql",          cJSON_CreateString(pRequest->sqlstr));