Abstract: The double-current traction power supply system based on static var generator can be used in the power supply section where AC and DC power supply system coexist, and can also provide factory test for multi-system locomotive, reduce power supply equipment, improve efficiency, and solve the negative sequence power quality problem. The structure of the double-current power supply system is proposed, and the basic principles of the two operating modes are studied respectively according to the operating conditions of the load. The negative sequence compensation mathematical model is constructed and the calculation formula of the capacity of the static var generator is derived. Based on instantaneous reactive power theory, the control strategy of static var generator in this scheme is studied. Built the simulation model, the simulation results show that under different load operating conditions, the double-current power supply system can not only provide running power for AC load and DC load, but also manage the negative sequence at the point of common coupling, which verifies the correctness and feasibility of the compensation scheme.