Load balancing is a critical demand in Provider Backbone Bridge Network (PBBN). Equal Cost Multiple Path (ECMP) in Shortest Path Bridging (SPB), described in the IEEE 802.1aq standard, is known as a scheme to gain better load balancing comparing to other schemes by enabling bridge to use multiple equal shortest paths between it and other bridges. In ECMP, up to 16 shortest paths are available for traffic forwarding. However, in a big network, in which there are more than 16 shortest paths between some two bridges, ECMP becomes limited. Therefore, the authors proposed an improved method applying ECMP in a big network.