diff --git a/mishards/exception_codes.py b/mishards/exception_codes.py
index ecb2469562..bdd4572dd5 100644
--- a/mishards/exception_codes.py
+++ b/mishards/exception_codes.py
@@ -7,3 +7,4 @@ DB_ERROR_CODE = 10003
 TABLE_NOT_FOUND_CODE = 20001
 INVALID_ARGUMENT_CODE = 20002
 INVALID_DATE_RANGE_CODE = 20003
+INVALID_TOPK_CODE = 20004
diff --git a/mishards/exception_handlers.py b/mishards/exception_handlers.py
index 1e5ffb3529..c79a6db5a3 100644
--- a/mishards/exception_handlers.py
+++ b/mishards/exception_handlers.py
@@ -58,6 +58,12 @@ def TableNotFoundErrorHandler(err):
     return resp_handler(err, status_pb2.TABLE_NOT_EXISTS)
 
 
+@server.errorhandler(exceptions.InvalidTopKError)
+def InvalidTopKErrorHandler(err):
+    logger.error(err)
+    return resp_handler(err, status_pb2.ILLEGAL_TOPK)
+
+
 @server.errorhandler(exceptions.InvalidArgumentError)
 def InvalidArgumentErrorHandler(err):
     logger.error(err)
diff --git a/mishards/exceptions.py b/mishards/exceptions.py
index acd9372d6a..72839f88d2 100644
--- a/mishards/exceptions.py
+++ b/mishards/exceptions.py
@@ -26,6 +26,10 @@ class TableNotFoundError(BaseException):
     code = codes.TABLE_NOT_FOUND_CODE
 
 
+class InvalidTopKError(BaseException):
+    code = codes.INVALID_TOPK_CODE
+
+
 class InvalidArgumentError(BaseException):
     code = codes.INVALID_ARGUMENT_CODE
 
diff --git a/mishards/service_handler.py b/mishards/service_handler.py
index 44e1d8cf7b..5e91c14f14 100644
--- a/mishards/service_handler.py
+++ b/mishards/service_handler.py
@@ -20,6 +20,7 @@ logger = logging.getLogger(__name__)
 
 class ServiceHandler(milvus_pb2_grpc.MilvusServiceServicer):
     MAX_NPROBE = 2048
+    MAX_TOPK = 2048
 
     def __init__(self, tracer, router, max_workers=multiprocessing.cpu_count(), **kwargs):
         self.table_meta = {}
@@ -246,6 +247,10 @@ class ServiceHandler(milvus_pb2_grpc.MilvusServiceServicer):
             raise exceptions.InvalidArgumentError(
                 message='Invalid nprobe: {}'.format(nprobe), metadata=metadata)
 
+        if topk > self.MAX_TOPK or topk <= 0:
+            raise exceptions.InvalidTopKError(
+                message='Invalid topk: {}'.format(topk), metadata=metadata)
+
         table_meta = self.table_meta.get(table_name, None)
 
         if not table_meta:
diff --git a/mishards/utilities.py b/mishards/utilities.py
index c08d0d42df..42e982b5f1 100644
--- a/mishards/utilities.py
+++ b/mishards/utilities.py
@@ -2,12 +2,12 @@ import datetime
 from mishards import exceptions
 
 
-def format_date(self, start, end):
+def format_date(start, end):
     return ((start.year - 1900) * 10000 + (start.month - 1) * 100 + start.day,
             (end.year - 1900) * 10000 + (end.month - 1) * 100 + end.day)
 
 
-def range_to_date(self, range_obj, metadata=None):
+def range_to_date(range_obj, metadata=None):
     try:
         start = datetime.datetime.strptime(range_obj.start_date, '%Y-%m-%d')
         end = datetime.datetime.strptime(range_obj.end_date, '%Y-%m-%d')
@@ -17,4 +17,4 @@ def range_to_date(self, range_obj, metadata=None):
             range_obj.start_date, range_obj.end_date),
             metadata=metadata)
 
-    return self.format_date(start, end)
+    return format_date(start, end)