diff --git a/paddle/operators/parallel_do_op.cc b/paddle/operators/parallel_do_op.cc
index fd48c1b54cb9cc45416d2fd8e9b1426d488e5d2d..6ac480b576c8841c9ff698cc7b04cc3b1c6e7990 100644
--- a/paddle/operators/parallel_do_op.cc
+++ b/paddle/operators/parallel_do_op.cc
@@ -47,7 +47,7 @@ void SplitTensorAndMoveTensorToScopes(
       LOG(INFO) << lod.dims();
     }
 
-    for (int i = 0; i < sub_scopes.size(); ++i) {
+    for (size_t i = 0; i < sub_scopes.size(); ++i) {
       *sub_scopes[i]->Var(argu)->GetMutable<LoDTensor>() = lod_tensors[i];
     }
   }
@@ -73,15 +73,14 @@ class ParallelDoOp : public framework::OperatorBase {
 
     auto &sub_scopes = *scope.FindVar(Output(kParallelScopes))
                             ->GetMutable<std::vector<framework::Scope *>>();
-    //    std::vector<framework::Scope *> sub_scopes;
-    for (int place_idx = 0; place_idx < places.size(); ++place_idx) {
+    for (size_t place_idx = 0; place_idx < places.size(); ++place_idx) {
       sub_scopes.push_back(&scope.NewScope());
     }
 
     SplitTensorAndMoveTensorToScopes(scope, sub_scopes, places,
                                      Inputs(kInputs));
 
-    for (int place_idx = 0; place_idx < places.size(); ++place_idx) {
+    for (size_t place_idx = 0; place_idx < places.size(); ++place_idx) {
       VLOG(3) << "Run " << place_idx;
 
       auto &place = places[place_idx];
@@ -163,17 +162,12 @@ class ParallelDoGradOp : public OperatorBase {
     }
 
     // exe run
-    for (int place_idx = 0; place_idx < places.size(); ++place_idx) {
+    for (size_t place_idx = 0; place_idx < places.size(); ++place_idx) {
       VLOG(3) << "Run " << place_idx;
 
       auto &place = places[place_idx];
       auto *cur_scope = sub_scopes[place_idx];
 
-      // copy parameter
-      if (dev_ctx.GetPlace() != place) {
-        PADDLE_THROW("Not Implemented");
-      }
-
       // execute
       auto executor = framework::Executor(place);
       executor.Run(*program, cur_scope, block->ID(),
@@ -181,6 +175,21 @@ class ParallelDoGradOp : public OperatorBase {
     }
 
     // merge grad
+    for (auto &s : Outputs(framework::GradVarName(kParameters))) {
+      LOG(INFO) << s;
+      // std::string s_buf = s + "@BUF";
+      // auto *t_buf = sub_scopes[0]->Var(s_buf)->GetMutable<LoDTensor>();
+      for (size_t place_idx = 1; place_idx < places.size(); ++place_idx) {
+        LOG(INFO) << place_idx;
+        LOG(INFO) << sub_scopes[place_idx]->FindVar(s)->Get<LoDTensor>();
+        // Copy grad[i] to grad_buf[0]
+
+        // sum_op
+      }
+
+      // Copy grad[0] to grad
+      // auto *t = scope.FindVar(s)->GetMutable<LoDTensor>();
+    }
   }
 };