diff --git a/include/libs/planner/planner.h b/include/libs/planner/planner.h
index f9c25c3ccc..3ca923b0aa 100644
--- a/include/libs/planner/planner.h
+++ b/include/libs/planner/planner.h
@@ -132,7 +132,7 @@ typedef struct SSubplan {
 typedef struct SQueryDag {
   uint64_t queryId;
   int32_t  numOfSubplans;
-  SArray  *pSubplans; // Element is SArray*, and nested element is SSubplan. The execution level of subplan, starting from 0.
+  SArray  *pSubplans; // SArray*<SArray*<SSubplan*>>. The execution level of subplan, starting from 0.
 } SQueryDag;
 
 struct SQueryNode;
@@ -159,8 +159,6 @@ int32_t qStringToSubplan(const char* str, SSubplan** subplan);
 
 void qDestroySubplan(SSubplan* pSubplan);
 
-char* qDagSerialize(const SQueryDag* pDag);
-
 /**
  * Destroy the physical plan.
  * @param pQueryPhyNode
diff --git a/source/libs/planner/src/physicalPlanJson.c b/source/libs/planner/src/physicalPlanJson.c
index 945c354284..9b2c9c1796 100644
--- a/source/libs/planner/src/physicalPlanJson.c
+++ b/source/libs/planner/src/physicalPlanJson.c
@@ -860,18 +860,33 @@ int32_t stringToSubplan(const char* str, SSubplan** subplan) {
 
 cJSON* qDagToJson(const SQueryDag* pDag) {
   cJSON* pRoot = cJSON_CreateObject();
+  if(pRoot == NULL) {
+    return NULL;
+  }
   cJSON_AddNumberToObject(pRoot, "numOfSubplans", pDag->numOfSubplans);
   cJSON_AddNumberToObject(pRoot, "queryId", pDag->queryId);
   cJSON *pLevels = cJSON_CreateArray();
+  if(pLevels == NULL) {
+    cJSON_Delete(pRoot);
+    return NULL;
+  }
   cJSON_AddItemToObject(pRoot, "pSubplans", pLevels);
   size_t level = taosArrayGetSize(pDag->pSubplans);
   for(size_t i = 0; i < level; i++) {
     const SArray* pSubplans = (const SArray*)taosArrayGetP(pDag->pSubplans, i);
     size_t num = taosArrayGetSize(pSubplans);
     cJSON* plansOneLevel = cJSON_CreateArray();
+    if(plansOneLevel == NULL) {
+      cJSON_Delete(pRoot);
+      return NULL;
+    }
     cJSON_AddItemToArray(pLevels, plansOneLevel);
     for(size_t j = 0; j < num; j++) {
       cJSON* pSubplan = subplanToJson((const SSubplan*)taosArrayGetP(pSubplans, j));
+      if(pSubplan == NULL) {
+        cJSON_Delete(pRoot);
+        return NULL;
+      }
       cJSON_AddItemToArray(plansOneLevel, pSubplan);
     }
   }
@@ -889,18 +904,34 @@ SQueryDag* qJsonToDag(const cJSON* pRoot) {
     return NULL;
   }
   pDag->numOfSubplans = cJSON_GetNumberValue(cJSON_GetObjectItem(pRoot, "numOfSubplans"));
+  pDag->queryId = cJSON_GetNumberValue(cJSON_GetObjectItem(pRoot, "queryId"));
   pDag->pSubplans = taosArrayInit(0, sizeof(SArray));
-  cJSON* pLevels = cJSON_GetObjectItem(pRoot, "numOfSubplans");
+  if (pDag->pSubplans == NULL) {
+    free(pDag);
+    return NULL;
+  }
+  cJSON* pLevels = cJSON_GetObjectItem(pRoot, "pSubplans");
   int level = cJSON_GetArraySize(pLevels);
   for(int i = 0; i < level; i++) {
+    SArray* plansOneLevel = taosArrayInit(0, sizeof(void*));
+    if(plansOneLevel == NULL) {
+      for(int j = 0; j < i; j++) {
+        taosArrayDestroy(taosArrayGetP(pDag->pSubplans, j));
+      }
+      taosArrayDestroy(pDag->pSubplans);
+      free(pDag);
+      return NULL;
+    }
     cJSON* pItem = cJSON_GetArrayItem(pLevels, i);
     int sz = cJSON_GetArraySize(pItem);
     for(int j = 0; j < sz; j++) {
       cJSON* pSubplanJson = cJSON_GetArrayItem(pItem, j);
       SSubplan* pSubplan = subplanFromJson(pSubplanJson);
-    } 
+      taosArrayPush(plansOneLevel, &pSubplan);
+    }
+    taosArrayPush(pDag->pSubplans, plansOneLevel);
   }
-  return NULL;
+  return pDag;
 }
 
 SQueryDag* qStringToDag(const char* pStr) {
diff --git a/source/libs/planner/test/phyPlanTests.cpp b/source/libs/planner/test/phyPlanTests.cpp
index d0f6fd5adf..02d06bb49d 100644
--- a/source/libs/planner/test/phyPlanTests.cpp
+++ b/source/libs/planner/test/phyPlanTests.cpp
@@ -83,7 +83,7 @@ protected:
     }
   }
 
-  SQueryDag* reslut() {
+  SQueryDag* result() {
     return dag_.get();
   }
 
@@ -149,16 +149,23 @@ TEST_F(PhyPlanTest, tableScanTest) {
   pushScan("test", "t1", QNODE_TABLESCAN);
   ASSERT_EQ(run(), TSDB_CODE_SUCCESS);
   explain();
-  SQueryDag* dag = reslut();
+  SQueryDag* dag = result();
   // todo check
 }
 
+TEST_F(PhyPlanTest, serializeTest) {
+  pushScan("test", "t1", QNODE_TABLESCAN);
+  ASSERT_EQ(run(), TSDB_CODE_SUCCESS);
+  SQueryDag* dag = result();
+  cout << qDagToString(dag) << endl;
+}
+
 // select * from supertable
 TEST_F(PhyPlanTest, superTableScanTest) {
   pushScan("test", "st1", QNODE_TABLESCAN);
   ASSERT_EQ(run(), TSDB_CODE_SUCCESS);
   explain();
-  SQueryDag* dag = reslut();
+  SQueryDag* dag = result();
   // todo check
 }
 
@@ -166,6 +173,6 @@ TEST_F(PhyPlanTest, superTableScanTest) {
 TEST_F(PhyPlanTest, insertTest) {
   ASSERT_EQ(run("test", "insert into t1 values (now, 1, \"beijing\")"), TSDB_CODE_SUCCESS);
   explain();
-  SQueryDag* dag = reslut();
+  SQueryDag* dag = result();
   // todo check
 }