With the development of urban rail transit in the direction of high-speed, heavy-load, large capacity and high-density, DC traction power supply system which is responsible for providing power for a variety of operation equipment needs to meet higher requirements in terms of safety and reliability. With efficient, safe and stable power supply demand of urban rail transit traction system, the composition of DC traction power supply system and the principle of 24-pulse rectifier transformer are introduced. Then, based on MATLAB/Simulink platform, traction substation rectifier, metro and catenary are modeled successively, and urban rail transit DC traction power supply system simulation model is built also. By dynamic simulation of train in starting and stable running stage, this paper verifies the correctness and effectiveness of simulation model, and gives a useful research platform and more referenced data on analysis of various fault of metro power supply system.