The invention provides a network load balancing device and method. The device comprises a topology discovery module, a traffic statistics module, a large flow monitoring module, a load balancing rerouting module and a path calculation module, wherein the topology discovery module is configured to acquire network topology information and network parameter information, and the network parameter information includes energy consumption information of each switch in a network and capacity information of each link in the network; the traffic statistics module is configured to acquire network trafficinformation; the large flow monitoring module is configured to determine a large flow and a small flow on each link based on the network traffic information; the load balancing rerouting module is configured to calculate the load balancing degree of the links in the network based on the network topology information, the network parameter information and the network traffic information to determine an overload link; and the path calculation module is configured to determine a scheduling path of the large flow in the overload link based on the energy consumption information of the switches in the network and the network traffic information and form a new flow table.