Considering the current status that the electro-mechanical transient simulation and electromagnetic transient simulation are independent relatively and respectively in power system,and based on the actual requirements for both electro-mechanical transient and electromagnetic transient simulations,this paper proposes a data system for the conversion between electromechanical transient and electromagnetic transient sim-ulations based on PSS/E and EMT.The system establishes a contact between electromechanical transient and electromagnetic transient simulation with data conversion.The actual application of the system in Shanghai Power Grid suggests the system can convert the electromechanical transient data into electromagnetic transient data accurately.