diff --git a/apps/emqx_connector/src/emqx_connector_mongo.erl b/apps/emqx_connector/src/emqx_connector_mongo.erl
index 4af339538..36ea01db2 100644
--- a/apps/emqx_connector/src/emqx_connector_mongo.erl
+++ b/apps/emqx_connector/src/emqx_connector_mongo.erl
@@ -62,7 +62,8 @@ fields(sharded) ->
     , {servers, fun servers/1}
     ] ++ mongo_fields();
 fields(topology) ->
-    [ {max_overflow, fun emqx_connector_schema_lib:pool_size/1}
+    [ {pool_size, fun emqx_connector_schema_lib:pool_size/1}
+    , {max_overflow, fun emqx_connector_schema_lib:pool_size/1}
     , {overflow_ttl, fun duration/1}
     , {overflow_check_period, fun duration/1}
     , {local_threshold_ms, fun duration/1}
@@ -81,6 +82,8 @@ mongo_fields() ->
     , {auth_source, #{type => binary(),
                       nullable => true}}
     , {database, fun emqx_connector_schema_lib:database/1}
+    , {topology, #{type => hoconsc:ref(?MODULE, topology),
+                   nullable => true}}
     ] ++
     emqx_connector_schema_lib:ssl_fields().
 
@@ -170,9 +173,10 @@ do_start(InstId, Opts0, Config = #{mongo_type := Type,
                       ];
                   false -> [{ssl, false}]
               end,
+    Topology= maps:get(topology, Config, #{}), 
     Opts = Opts0 ++
            [{pool_size, PoolSize},
-            {options, init_topology_options(maps:to_list(Config), [])},
+            {options, init_topology_options(maps:to_list(Topology), [])},
             {worker_options, init_worker_options(maps:to_list(Config), SslOpts)}],
     %% test the connection
     TestOpts = case maps:is_key(server, Config) of