For the auxiliary converter system of SS4B locomotive of Shen-Shuo railway, there are many electric devices which are scattered on the locomotive with the disadvantages of complex wiring, being difficult to control as well as inconvenience to debug. An application control design of locomotive auxiliary converter based on CAN bus and DSP chip was presented. The system overall structure and CAN communication protocol, hardware circuit and software flow were introduced. The actual operation results showed that the distributed control system based on CAN bus could realize the centralized control of decentralized installation equipment on the locomotive, and perform the functions of long distance, high reliability communication and remote monitoring and operation as well, which greatly improved the control performance of the electric locomotive.