Aiming at the problems of uneven load distribution and high packet loss rate in traditional power communication network routing strategy, based on software defined networks, a QoS routing strategy for power communication network based on improved Lagrange relaxation algorithm is proposed.The routing model is established with the constraints of link delay, available bandwidth and packet loss rate, the improved Lagrange relaxation algorithm is used for path selection.The feasibility of this method is verified by simulation and comparison with traditional routing methods.The results show that compared with the traditional routing strategy, this method can plan the path that meets the QoS requirements, the load distribution is more balanced, and the service packet loss rate is effectively reduced, packet loss rate is reduced from 45% to 0.1%, it has certain practical value.