diff --git a/TinySTL/Detail/Graph.impl.h b/TinySTL/Detail/Graph.impl.h
index 25e6edb..ffe22ac 100644
--- a/TinySTL/Detail/Graph.impl.h
+++ b/TinySTL/Detail/Graph.impl.h
@@ -101,12 +101,33 @@ namespace TinySTL{
 			auto nodes = adjacent_nodes(start->first);
 			func(*start);
 			visited.insert(start->first);
-			for (auto& n : nodes){
+			for (const auto& n : nodes){
 				if (visited.count(n.first) == 0)//has not visited
 					DFS(n.first, func);
 			}
 		}
 		template<class Index, class Value, class EqualFunc>
+		void graph<Index, Value, EqualFunc>::BFS(const Index& index, visiter_func_type func){
+			node *start = &(get_node(index));
+			Unordered_set<Index, std::hash<Index>, EqualFunc> visited(7);
+
+			auto nodes = adjacent_nodes(start->first);
+			func(*start);
+			visited.insert(start->first);
+			do{
+				node_sets temp;
+				for (auto it = nodes.begin(); it != nodes.end(); ++it){
+					if (visited.count(it->first) == 0){//has not visited
+						func(*it);
+						visited.insert(it->first);
+						auto s = adjacent_nodes(it->first);						
+						temp.insert(temp.end(), s.begin(), s.end());
+					}
+				}
+				nodes = temp;
+			} while (!nodes.empty());
+		}
+		template<class Index, class Value, class EqualFunc>
 		string graph<Index, Value, EqualFunc>::to_string(){
 			string str;
 			std::ostringstream oss;
diff --git a/TinySTL/Graph.h b/TinySTL/Graph.h
index 363abcd..fb41590 100644
--- a/TinySTL/Graph.h
+++ b/TinySTL/Graph.h
@@ -40,12 +40,14 @@ namespace TinySTL{
 
 			//node can be not in the graph
 			virtual void add_node(const node& item, const node_sets& nodes) = 0;
-			//node of the index must in the graph
-			virtual void add_node(const Index& index, const node_sets& nodes) = 0;
 			//virtual void delte_node(const node& item) = 0;
 
+			//node of the index must in the graph
+			virtual void add_node(const Index& index, const node_sets& nodes) = 0;
+			//virtual void delte_node(const Index& index) = 0;
+
 			void DFS(const Index& index, visiter_func_type func);
-			//virtual void BFS(visiter_func_type func) = 0;
+			void BFS(const Index& index, visiter_func_type func);
 
 			node& new_node(const Index& index, const Value& val);
 			void del_node(node *p);