diff --git a/CHANGELOG.md b/CHANGELOG.md
index a20f36ec11..2511c98150 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,7 @@ Please mark all change in change log and use the issue from GitHub
 ## Feature
 
 ## Improvement
+-   \#3213 Allow users to specify a distance type at runtime for Flat index
 
 ## Task
 
diff --git a/core/src/db/engine/ExecutionEngineImpl.cpp b/core/src/db/engine/ExecutionEngineImpl.cpp
index cbc7aa9194..fee486c532 100644
--- a/core/src/db/engine/ExecutionEngineImpl.cpp
+++ b/core/src/db/engine/ExecutionEngineImpl.cpp
@@ -1158,7 +1158,10 @@ ExecutionEngineImpl::Search(int64_t n, const float* data, int64_t k, const milvu
     }
 
     milvus::json conf = extra_params;
+    if (conf.contains(knowhere::Metric::TYPE))
+        MappingMetricType(conf[knowhere::Metric::TYPE], conf);
     conf[knowhere::meta::TOPK] = k;
+
     auto adapter = knowhere::AdapterMgr::GetInstance().GetAdapter(index_->index_type());
     if (!adapter->CheckSearch(conf, index_->index_type(), index_->index_mode())) {
         LOG_ENGINE_ERROR_ << LogOut("[%s][%ld] Illegal search params", "search", 0);
@@ -1197,6 +1200,8 @@ ExecutionEngineImpl::Search(int64_t n, const uint8_t* data, int64_t k, const mil
     }
 
     milvus::json conf = extra_params;
+    if (conf.contains(knowhere::Metric::TYPE))
+        MappingMetricType(conf[knowhere::Metric::TYPE], conf);
     conf[knowhere::meta::TOPK] = k;
     auto adapter = knowhere::AdapterMgr::GetInstance().GetAdapter(index_->index_type());
     if (!adapter->CheckSearch(conf, index_->index_type(), index_->index_mode())) {
diff --git a/core/src/index/knowhere/knowhere/index/vector_index/IndexBinaryIDMAP.cpp b/core/src/index/knowhere/knowhere/index/vector_index/IndexBinaryIDMAP.cpp
index 056a955abe..5a3ebb923a 100644
--- a/core/src/index/knowhere/knowhere/index/vector_index/IndexBinaryIDMAP.cpp
+++ b/core/src/index/knowhere/knowhere/index/vector_index/IndexBinaryIDMAP.cpp
@@ -53,8 +53,8 @@ BinaryIDMAP::Query(const DatasetPtr& dataset_ptr, const Config& config) {
     auto p_id = (int64_t*)malloc(p_id_size);
     auto p_dist = (float*)malloc(p_dist_size);
 
-    QueryImpl(rows, (uint8_t*)p_data, k, p_dist, p_id, Config());
-
+    //    QueryImpl(rows, (uint8_t*)p_data, k, p_dist, p_id, Config());
+    QueryImpl(rows, (uint8_t*)p_data, k, p_dist, p_id, config);
     auto ret_ds = std::make_shared<Dataset>();
     if (index_->metric_type == faiss::METRIC_Hamming) {
         auto pf_dist = (float*)malloc(p_dist_size);
@@ -214,7 +214,13 @@ void
 BinaryIDMAP::QueryImpl(int64_t n, const uint8_t* data, int64_t k, float* distances, int64_t* labels,
                        const Config& config) {
     int32_t* pdistances = (int32_t*)distances;
+
+    auto flat_index = dynamic_cast<faiss::IndexBinaryIDMap*>(index_.get())->index;
+    auto default_type = flat_index->metric_type;
+    if (config.contains(Metric::TYPE))
+        flat_index->metric_type = GetMetricType(config[Metric::TYPE].get<std::string>());
     index_->search(n, (uint8_t*)data, k, pdistances, labels, bitset_);
+    flat_index->metric_type = default_type;
 }
 
 }  // namespace knowhere
diff --git a/core/src/index/knowhere/knowhere/index/vector_index/IndexIDMAP.cpp b/core/src/index/knowhere/knowhere/index/vector_index/IndexIDMAP.cpp
index 612de45547..cf09eeaccb 100644
--- a/core/src/index/knowhere/knowhere/index/vector_index/IndexIDMAP.cpp
+++ b/core/src/index/knowhere/knowhere/index/vector_index/IndexIDMAP.cpp
@@ -105,8 +105,8 @@ IDMAP::Query(const DatasetPtr& dataset_ptr, const Config& config) {
     auto p_id = (int64_t*)malloc(p_id_size);
     auto p_dist = (float*)malloc(p_dist_size);
 
-    QueryImpl(rows, (float*)p_data, k, p_dist, p_id, Config());
-
+    //    QueryImpl(rows, (float*)p_data, k, p_dist, p_id, Config());
+    QueryImpl(rows, (float*)p_data, k, p_dist, p_id, config);
     auto ret_ds = std::make_shared<Dataset>();
     ret_ds->Set(meta::IDS, p_id);
     ret_ds->Set(meta::DISTANCE, p_dist);
@@ -221,7 +221,12 @@ IDMAP::GetVectorById(const DatasetPtr& dataset_ptr, const Config& config) {
 
 void
 IDMAP::QueryImpl(int64_t n, const float* data, int64_t k, float* distances, int64_t* labels, const Config& config) {
+    auto flat_index = dynamic_cast<faiss::IndexIDMap*>(index_.get())->index;
+    auto default_type = flat_index->metric_type;
+    if (config.contains(Metric::TYPE))
+        flat_index->metric_type = GetMetricType(config[Metric::TYPE].get<std::string>());
     index_->search(n, (float*)data, k, distances, labels, bitset_);
+    flat_index->metric_type = default_type;
 }
 
 }  // namespace knowhere
diff --git a/core/src/index/knowhere/knowhere/index/vector_index/gpu/IndexGPUIDMAP.cpp b/core/src/index/knowhere/knowhere/index/vector_index/gpu/IndexGPUIDMAP.cpp
index 5bcc288c32..f91afa19a6 100644
--- a/core/src/index/knowhere/knowhere/index/vector_index/gpu/IndexGPUIDMAP.cpp
+++ b/core/src/index/knowhere/knowhere/index/vector_index/gpu/IndexGPUIDMAP.cpp
@@ -17,6 +17,7 @@
 #include <faiss/gpu/GpuCloner.h>
 #endif
 #include <fiu-local.h>
+#include <string>
 
 #include "knowhere/common/Exception.h"
 #include "knowhere/index/vector_index/IndexIDMAP.h"
@@ -105,7 +106,13 @@ GPUIDMAP::GetRawIds() {
 void
 GPUIDMAP::QueryImpl(int64_t n, const float* data, int64_t k, float* distances, int64_t* labels, const Config& config) {
     ResScope rs(res_, gpu_id_);
+
+    auto flat_index = dynamic_cast<faiss::IndexIDMap*>(index_.get())->index;
+    auto default_type = flat_index->metric_type;
+    if (config.contains(Metric::TYPE))
+        flat_index->metric_type = GetMetricType(config[Metric::TYPE].get<std::string>());
     index_->search(n, (float*)data, k, distances, labels, bitset_);
+    flat_index->metric_type = default_type;
 }
 
 void
diff --git a/core/src/scheduler/task/SearchTask.cpp b/core/src/scheduler/task/SearchTask.cpp
index e9dd032f1e..521c81f179 100644
--- a/core/src/scheduler/task/SearchTask.cpp
+++ b/core/src/scheduler/task/SearchTask.cpp
@@ -22,6 +22,7 @@
 
 #include "db/Utils.h"
 #include "db/engine/EngineFactory.h"
+#include "index/knowhere/knowhere/index/vector_index/helpers/IndexParameter.h"
 #include "metrics/Metrics.h"
 #include "scheduler/SchedInst.h"
 #include "scheduler/job/SearchJob.h"
@@ -122,6 +123,9 @@ XSearchTask::XSearchTask(const std::shared_ptr<server::Context>& context, Segmen
         milvus::json json_params;
         if (!file_->index_params_.empty()) {
             json_params = milvus::json::parse(file_->index_params_);
+            if (json_params.contains(knowhere::Metric::TYPE) &&
+                (engine_type == EngineType::FAISS_BIN_IDMAP || engine_type == EngineType::FAISS_IDMAP))
+                ascending_reduce = json_params[knowhere::Metric::TYPE] != static_cast<int>(MetricType::IP);
         }
         //        if (auto job = job_.lock()) {
         //            auto search_job = std::static_pointer_cast<scheduler::SearchJob>(job);