diff --git a/chatlearn/synchronizer/parameter_sync.py b/chatlearn/synchronizer/parameter_sync.py
index 2267d80f..6daa5a8f 100644
--- a/chatlearn/synchronizer/parameter_sync.py
+++ b/chatlearn/synchronizer/parameter_sync.py
@@ -1180,6 +1180,15 @@ def setup_rank_mapping(self):
             f"greater or equal to expert parallel world size for inference ({self.num_dst_expert_parallel}) with HEP enabled."
         )
         if self.dst_model.use_vllm_backend:
+            if (
+                self.hep_num_mapping != 1
+                and get_args().runtime_args.routed_expert_regrouping_comm_type == ROUTED_EXPERT_REGROUPING_COMM_TYPE.ALLTOALL
+            ):
+                raise NotImplementedError(
+                    "all-to-all routed expert weight is only supported when src TP size * src EP size = dst TP size. "
+                    "Please consider setting `routed_expert_regrouping_comm_type` to allgather or adjusting the model's parallel size."
+                )
+
             if self.tp_num_mapping == 1:
                 if self.ep_num_mapping == 1:
                     self.build_rank_mapping()
diff --git a/chatlearn/utils/arguments.py b/chatlearn/utils/arguments.py
index c7d89e50..320a4d3d 100644
--- a/chatlearn/utils/arguments.py
+++ b/chatlearn/utils/arguments.py
@@ -311,7 +311,7 @@ class RuntimeConfig(BaseConfig):
     #: parameter sync max workers
     param_sync_max_workers: int = None
     #: communication type to regroup routed experts, allgather/alltoall
-    routed_expert_regrouping_comm_type: str = ROUTED_EXPERT_REGROUPING_COMM_TYPE.ALLTOALL
+    routed_expert_regrouping_comm_type: str = ROUTED_EXPERT_REGROUPING_COMM_TYPE.ALLGATHER
     #: max number of relay episodes, if `max_relay_episode` is set to -1, then relay all episodes
     #: if `max_relay_episode` is set to 0, then relay is disabled
     max_relay_episode: int = 0
diff --git a/chatlearn/utils/constant.py b/chatlearn/utils/constant.py
index 4ee59907..efa1e7a6 100644
--- a/chatlearn/utils/constant.py
+++ b/chatlearn/utils/constant.py
@@ -61,5 +61,5 @@ class PARAM_SYNC_COMM_TYPE(str, Enum):
 
 class ROUTED_EXPERT_REGROUPING_COMM_TYPE(str, Enum):
     """communication type of routed expert regrouping."""
-    ALLTOALL = "alltoall"
     ALLGATHER = "allgather"
+    ALLTOALL = "alltoall"
diff --git a/tests/test_hep_eptp_vllm_tp.py b/tests/test_hep_eptp_vllm_tp.py
index 847234c4..af3a61fc 100644
--- a/tests/test_hep_eptp_vllm_tp.py
+++ b/tests/test_hep_eptp_vllm_tp.py
@@ -195,21 +195,21 @@ def test_hep_eptp_vllm_tp_dst_ep1_tp2_pp1_src_ep4_tp2_pp1():
     assert param_sync_group.ep_num_mapping == tuples[0] / tuples[3]
     assert param_sync_group.tp_num_mapping == tuples[1] // tuples[4]
 
-    # Judge alltoall actors
-    alltoall_actors = param_sync_group.send_actors_to_regroup_routed_experts
+    # Judge allgather actors
+    allgather_actors = param_sync_group.send_actors_to_regroup_routed_experts
     actor2rank = param_sync_group.actor2rank
 
-    assert param_sync_group._comm_type_to_regroup_routed_experts == "alltoall"
-    assert len(alltoall_actors) == 1
-    assert len(alltoall_actors[0]) == 8 # all src ranks should all-to-all routed experts
+    assert param_sync_group._comm_type_to_regroup_routed_experts == "allgather"
+    assert len(allgather_actors) == 1
+    assert len(allgather_actors[0]) == 8 # all src ranks should all-to-all routed experts
     assert len(actor2rank) == 16 # all of the 16 actors should have rank
     assert len(set(list(actor2rank.values()))) == len(actor2rank) # all ranks should be unique
 
-    alltoall_actor_ranks = []
-    for actor in alltoall_actors[0]:
-        alltoall_actor_ranks.append(actor2rank[actor])
+    allgather_actor_ranks = []
+    for actor in allgather_actors[0]:
+        allgather_actor_ranks.append(actor2rank[actor])
 
-    assert alltoall_actor_ranks == [0, 1, 2, 3, 4, 5, 6, 7]
+    assert allgather_actor_ranks == [0, 1, 2, 3, 4, 5, 6, 7]
 
     # Judge src->dst rank mappings
     comm_pairs = []
diff --git a/tests/test_hep_eptppp_vllm_tp.py b/tests/test_hep_eptppp_vllm_tp.py
index ce767fd0..4cf6ee68 100644
--- a/tests/test_hep_eptppp_vllm_tp.py
+++ b/tests/test_hep_eptppp_vllm_tp.py
@@ -197,24 +197,24 @@ def test_hep_eptppp_vllm_tp_dst_ep1_tp2_pp1_src_ep2_tp2_pp2():
     assert param_sync_group.ep_num_mapping == tuples[0] / tuples[3]
     assert param_sync_group.tp_num_mapping == tuples[1] // tuples[4]
 
-    # Judge alltoall actors
-    alltoall_actors = param_sync_group.send_actors_to_regroup_routed_experts
+    # Judge allgather actors
+    allgather_actors = param_sync_group.send_actors_to_regroup_routed_experts
     actor2rank = param_sync_group.actor2rank
 
-    assert param_sync_group._comm_type_to_regroup_routed_experts == "alltoall"
-    assert len(alltoall_actors) == 2
-    assert len(alltoall_actors[0]) == 4 # prev 4 src ranks should all-to-all routed experts
-    assert len(alltoall_actors[1]) == 4 # last 4 src ranks should all-to-all routed experts
+    assert param_sync_group._comm_type_to_regroup_routed_experts == "allgather"
+    assert len(allgather_actors) == 2
+    assert len(allgather_actors[0]) == 4 # prev 4 src ranks should all-to-all routed experts
+    assert len(allgather_actors[1]) == 4 # last 4 src ranks should all-to-all routed experts
     assert len(actor2rank) == 16 # all of the 16 actors should have rank
     assert len(set(list(actor2rank.values()))) == len(actor2rank) # all ranks should be unique
 
-    alltoall_actor_ranks = []
-    for actor_list in alltoall_actors:
-        alltoall_actor_ranks.append([])
+    allgather_actor_ranks = []
+    for actor_list in allgather_actors:
+        allgather_actor_ranks.append([])
         for actor in actor_list:
-            alltoall_actor_ranks[-1].append(actor2rank[actor])
+            allgather_actor_ranks[-1].append(actor2rank[actor])
 
-    assert alltoall_actor_ranks == [[0, 1, 2, 3], [4, 5, 6, 7]]
+    assert allgather_actor_ranks == [[0, 1, 2, 3], [4, 5, 6, 7]]
 
     # Judge src->dst rank mappings
     comm_pairs = []
diff --git a/tests/test_hep_tp_vllm_tp.py b/tests/test_hep_tp_vllm_tp.py
index 02a1406c..6027c97b 100644
--- a/tests/test_hep_tp_vllm_tp.py
+++ b/tests/test_hep_tp_vllm_tp.py
@@ -195,24 +195,24 @@ def test_hep_tp_vllm_tp_dst_ep1_tp4_pp1_src_ep1_tp4_pp1():
     assert param_sync_group.ep_num_mapping == tuples[0] / tuples[3]
     assert param_sync_group.tp_num_mapping == tuples[1] // tuples[4]
 
-    # Judge alltoall actors
-    alltoall_actors = param_sync_group.send_actors_to_regroup_routed_experts
+    # Judge allgather actors
+    allgather_actors = param_sync_group.send_actors_to_regroup_routed_experts
     actor2rank = param_sync_group.actor2rank
 
-    assert param_sync_group._comm_type_to_regroup_routed_experts == "alltoall"
-    assert len(alltoall_actors) == 2
-    assert len(alltoall_actors[0]) == 4 # prev 4 src ranks should all-to-all routed experts
-    assert len(alltoall_actors[1]) == 4 # last 4 src ranks should all-to-all routed experts
+    assert param_sync_group._comm_type_to_regroup_routed_experts == "allgather"
+    assert len(allgather_actors) == 2
+    assert len(allgather_actors[0]) == 4 # prev 4 src ranks should all-to-all routed experts
+    assert len(allgather_actors[1]) == 4 # last 4 src ranks should all-to-all routed experts
     assert len(actor2rank) == 16 # all of the 16 actors should have rank
     assert len(set(list(actor2rank.values()))) == len(actor2rank) # all ranks should be unique
 
-    alltoall_actor_ranks = []
-    for actor_list in alltoall_actors:
-        alltoall_actor_ranks.append([])
+    allgather_actor_ranks = []
+    for actor_list in allgather_actors:
+        allgather_actor_ranks.append([])
         for actor in actor_list:
-            alltoall_actor_ranks[-1].append(actor2rank[actor])
+            allgather_actor_ranks[-1].append(actor2rank[actor])
 
-    assert alltoall_actor_ranks == [[0, 1, 2, 3], [4, 5, 6, 7]]
+    assert allgather_actor_ranks == [[0, 1, 2, 3], [4, 5, 6, 7]]
 
     # Judge src->dst rank mappings
     comm_pairs = []