To ensure the reliability of electric power dispatching data network, a congestion avoidance algorithm based on the dispatching data service priority is proposed. Firstly, according to different requirements for the delay and bandwidth, the dispatching data services can be divided into several services with different priorities. In accordance with the service priorities, the positions of data packets are adjusted in the serious or moderate congestion node cache. The services with low priority are discarded, which are located after serious congestion threshold, and their source nodes are informed to choose route. Then, the fitness function is built and the optimal routing is selected employing binary particle swarm optimization (BPSO) algorithm. Simulation results show that the quality of service (QoS) of the services with high priority is firstly ensured. Meanwhile, the network resource can be optimized and network loads can be balanced.