Abstract: In smart grid, a lot of overloaded devices and optical cables are overloaded when transporting differential protection traffic with optical fiber channels. A multi-network load balancing model with traffic mutex routing and constrained facility load is established, and an integer linear programming algorithm that implements load balancing in multi-networks is presented. The algorithm was used to solve an example network of multiple power fiber communication networks in a province of China. Numerical results show that the proposed algorithm can greatly reduce the number of overload facilities (comparing with the current routing method, the number of overloaded facilities of interruptible protection traffic, the main optimization objective, is reduced by about 67%), and transfer traffic in high-load facilities to low-load ones.