Network system and load balance method

Disclosed are a network system and a load balance method. The load balance method includes: a controller receives identification information so as to construct a network topology and receives support speeds of connection ends; the controller monitors an average traffic of the connection ends; when the average traffic of one of the connection ends in a node exceeds a congestion threshold, the controller finds a maximum traffic packet flow in packet flows which pass the connection end, the average traffic of which exceeds the congestion threshold; according to the maximum traffic packet flow and the network topology, a shortest path algorithm is performed and calculated connection ends do not include the connection end, the average traffic of which exceeds the congestion threshold; and the controller obtains a new transmission path.