Abstract: The load process simulation of traction power supply system of high-speed railway mainly includes traction load power calculation during the EMU running and power flow calculation of traction power supply system. A traction calculation model was established to obtain the electrical load characteristics during the EMU running. Based on the multi-conductor transmission line model, an equivalent circuit of traction network was established, and based on the general transformation relation of the electric quantities of traction substation, the equivalent circuit of traction substation was established. Based on the traction load power, power flow calculation of traction power supply system could be carried out, the change of voltage and current of traction power supply system could be obtained. On this basis, a load process simulation program of high-speed railway traction power supply system was compiled, and the simulation program was used to simulate the traction power supply system of Dengjiashan of the Changsha—Kunming Passenger Line which was the first high-speed railway in Yunnan Province. The simulation results were consistent with the actual test results which were made by China Academy of Railway Sciences. The load process simulation of traction power supply system of high-speed railway is of great significance to study the operation rules of traction power supply system of high-speed railway, check and verify the various power supply indexes in the power supply system.