diff --git a/core/src/db/merge/MergeLayerStrategy.cpp b/core/src/db/merge/MergeLayerStrategy.cpp
index f107280e5a00a60d9a98b3d2405b99ddc822eee5..8c88a785bfd998351605a7eab5c713b45a4346ae 100644
--- a/core/src/db/merge/MergeLayerStrategy.cpp
+++ b/core/src/db/merge/MergeLayerStrategy.cpp
@@ -20,7 +20,7 @@ namespace milvus {
 namespace engine {
 
 namespace {
-const int64_t FORCE_MERGE_THREASHOLD = 30;  // force merge files older this time(in second)
+const int64_t FORCE_MERGE_THREASHOLD = 30 * 1000 * 1000;  // force merge files older this time(in microsecond)
 
 using LayerGroups = std::map<int64_t, SegmentInfoList>;
 
@@ -80,7 +80,7 @@ MergeLayerStrategy::RegroupSegments(const Partition2SegmentsMap& part2segment, i
             }
 
             if (segments.size() == 1) {
-                if (now - segments[0].create_on_ > static_cast<int64_t>(FORCE_MERGE_THREASHOLD * 1000)) {
+                if (now - segments[0].create_on_ > FORCE_MERGE_THREASHOLD) {
                     force_list.swap(segments);
                 }
             }