diff --git a/cpp/CHANGELOG.md b/cpp/CHANGELOG.md
index 63f6999353..5bb6053d49 100644
--- a/cpp/CHANGELOG.md
+++ b/cpp/CHANGELOG.md
@@ -22,6 +22,7 @@ Please mark all change in change log and use the ticket from JIRA.
 - MS-364 - Modify tasktableitem in tasktable
 - MS-365 - Use tasktableitemptr instead in event
 - MS-366 - Implement TaskTable
+- MS-368 - Implement cost.cpp
 
 ## New Feature
 - MS-343 - Implement ResourceMgr
diff --git a/cpp/src/scheduler/Cost.cpp b/cpp/src/scheduler/Cost.cpp
index 14b56d98a5..724a717d2f 100644
--- a/cpp/src/scheduler/Cost.cpp
+++ b/cpp/src/scheduler/Cost.cpp
@@ -12,22 +12,40 @@ namespace milvus {
 namespace engine {
 
 std::vector<uint64_t>
-PickToMove(const TaskTable &task_table, const CacheMgr &cache_mgr, uint64_t limit) {
+PickToMove(TaskTable &task_table, const CacheMgr &cache_mgr, uint64_t limit) {
     std::vector<uint64_t> indexes;
+    for (uint64_t i = 0, count = 0; i < task_table.Size() && count < limit; ++i) {
+        if (task_table[i]->state == TaskTableItemState::LOADED) {
+            indexes.push_back(i);
+            ++count;
+        }
+    }
     return indexes;
 }
 
 
 std::vector<uint64_t>
-PickToLoad(const TaskTable &task_table, uint64_t limit) {
+PickToLoad(TaskTable &task_table, uint64_t limit) {
     std::vector<uint64_t> indexes;
+    for (uint64_t i = 0, count = 0; i < task_table.Size() && count < limit; ++i) {
+        if (task_table[i]->state == TaskTableItemState::START) {
+            indexes.push_back(i);
+            ++count;
+        }
+    }
     return indexes;
 }
 
 
 std::vector<uint64_t>
-PickToExecute(const TaskTable &task_table, uint64_t limit) {
+PickToExecute(TaskTable &task_table, uint64_t limit) {
     std::vector<uint64_t> indexes;
+    for (uint64_t i = 0, count = 0; i < task_table.Size() && count < limit; ++i) {
+        if (task_table[i]->state == TaskTableItemState::LOADED) {
+            indexes.push_back(i);
+            ++count;
+        }
+    }
     return indexes;
 }
 
diff --git a/cpp/src/scheduler/Cost.h b/cpp/src/scheduler/Cost.h
index 85414337bc..76f16d4d1d 100644
--- a/cpp/src/scheduler/Cost.h
+++ b/cpp/src/scheduler/Cost.h
@@ -23,7 +23,7 @@ namespace engine {
  * call from scheduler;
  */
 std::vector<uint64_t>
-PickToMove(const TaskTable &task_table, const CacheMgr &cache_mgr, uint64_t limit);
+PickToMove(TaskTable &task_table, const CacheMgr &cache_mgr, uint64_t limit);
 
 
 /*
@@ -32,7 +32,7 @@ PickToMove(const TaskTable &task_table, const CacheMgr &cache_mgr, uint64_t limi
  * I DONT SURE NEED THIS;
  */
 std::vector<uint64_t>
-PickToLoad(const TaskTable &task_table, uint64_t limit);
+PickToLoad(TaskTable &task_table, uint64_t limit);
 
 /*
  * select task to execute;
@@ -40,7 +40,7 @@ PickToLoad(const TaskTable &task_table, uint64_t limit);
  * I DONT SURE NEED THIS;
  */
 std::vector<uint64_t>
-PickToExecute(const TaskTable &task_table, uint64_t limit);
+PickToExecute(TaskTable &task_table, uint64_t limit);
 
 
 }
diff --git a/cpp/src/scheduler/TaskTable.h b/cpp/src/scheduler/TaskTable.h
index 21c376a627..528c2f3d5c 100644
--- a/cpp/src/scheduler/TaskTable.h
+++ b/cpp/src/scheduler/TaskTable.h
@@ -90,6 +90,14 @@ public:
     Size() {
         return table_.size();
     }
+public:
+    TaskTableItemPtr &
+    operator[](uint64_t index) {
+        return table_[index];
+    }
+
+    std::deque<TaskTableItemPtr>::iterator begin() { return table_.begin(); }
+    std::deque<TaskTableItemPtr>::iterator end() { return table_.end(); }
 
 public: