Abstract: When microgrids operate in different modes such as grid connection or islanding,the changes of network topology pose high requirements for the coordinated protection strategy of substation secondary systems. Therefore,a substation secondary system protection strategy based on combining the improved gray wolf optimization（GWO）and particle swarm optimization（PSO）algorithms is proposed. Firstly,the mathematical model is established with the goal of minimizing the total operating time of all relays in the substation;Then,for the coordination optimization problem of overcurrent relays,the gray wolf optimizer and particle swarm optimization are combined,the improved GWO-PSO algorithm are used to solve the model;Subsequently,a central protection center,intelligent electronic devices and communication channels are used to obtain and transmit real-time data,and relay protection strategies for substations in different modes of microgrids are proposed. The simulation results show that compared to traditional methods,the proposed method has faster calculation speed and can significantly improve the speed of protection system.