Aiming at the problem of the transient process during the electromechanical transient simulation cannot be reflected in great detail during the fault time and there is under reaction to AC system during electromagnetic transient simulation, analysis the electromagnetic-electromachanical transient hybrid simulation of data exchange of electromagnetic transient subnet and electromachanical transient subnet. Details of the electromagnetic - electromechanical transient hybrid simulation software ADPSS and the principle and process of electromagnetic - electromechanical transient hybrid simulation based ADPSS. Electromagnetic transient simulation, electromechanical transient simulation and electromagnetic-electromechanical transient hybrid simulation are performed respectively on Debao ±500KV HVDC system, the simulation result shows that electromagnetic - electromechanical transient hybrid simulation can be an effective response analysis of local electromagnetic transient process and AC system for large scale power grid, the simulation speed is fast, accurate and reliable.