diff --git a/pymilvus/client/prepare.py b/pymilvus/client/prepare.py
index d63f4427a..425c4f307 100644
--- a/pymilvus/client/prepare.py
+++ b/pymilvus/client/prepare.py
@@ -457,7 +457,7 @@ def search_requests_with_expr(cls, collection_name, data, anns_field, param, lim
             raise ParamError(message=f"Search params must be a dict, got {type(params)}")
         search_params = {
             "topk": limit,
-            "metric_type": param.get("metric_type", "L2"),
+            "metric_type": param.get("metric_type", ""),
             "params": params,
             "round_decimal": round_decimal,
             "offset": param.get("offset", 0),