diff --git a/src/client/src/tscUtil.c b/src/client/src/tscUtil.c
index 4ce80acd67e22b70fd9b3cd083b15f8e3e0581f3..c62c63088e51ea83ce6262c9f539701e71b7fb81 100644
--- a/src/client/src/tscUtil.c
+++ b/src/client/src/tscUtil.c
@@ -1474,7 +1474,12 @@ void tscFreeSubobj(SSqlObj* pSql) {
   tscDebug("0x%"PRIx64" start to free sub SqlObj, numOfSub:%d", pSql->self, pSql->subState.numOfSub);
 
   for(int32_t i = 0; i < pSql->subState.numOfSub; ++i) {
-    tscDebug("0x%"PRIx64" free sub SqlObj:0x%"PRIx64", index:%d", pSql->self, pSql->pSubs[i]->self, i);
+    if (pSql->pSubs[i] != NULL) {
+      tscDebug("0x%"PRIx64" free sub SqlObj:0x%"PRIx64", index:%d", pSql->self, pSql->pSubs[i]->self, i);
+    } else {
+      /* just for python error test case */
+      tscDebug("0x%"PRIx64" free sub SqlObj:0x0, index:%d", pSql->self, i);
+    }
     taos_free_result(pSql->pSubs[i]);
     pSql->pSubs[i] = NULL;
   }