Abstract: Large scale electromagnetic transient simulation of power grids requires enormous computing power, the computing power resources of state-region-province three-layer dispatching centers are difficult to meet the needs of power grid safety and stability simulation calculation, this paper designs a mechanism for the mutual benefit of electromagnetic transient simulation resources in state-region-province three-layer dispatching centers. Firstly, the principles of efficient, reliable, and flexible resource mutual are introduced. Then, the mechanism and key technologies for constructing a cross domain unified computing resource pool and scheduling cross domain batch electromagnetic transient simulation tasks were highlighted. The functional architecture and main functions of the three-layer scheduling resource mutual assistance electromagnetic transient cloud simulation platform were briefly introduced. Finally, the platform is applied in the State Grid Simulation Center, Central China Branch of State Grid Corporation of China, and State Grid Henan Electric Power Company, actual application data has proven the effectiveness of the method proposed in this paper.