Abstract: The braking system is a key component that affects the safe driving of railway locomotives. The development of braking technology has a decisive effect on the development of railway. CCBII braking system is controlled by computer, used for electrical command signal transmission, which is widely used in railway locomotives. The simulation study of this system has practical significance. This paper researched the automatic braking process of the CCBII braking system. The function of the key modules of automatic braking and the principle of service braking and emergency braking were analyzed. A simulation model which could visually present the pressure changes of the air circuit components was established by AMESim software. The simulation results of service braking and emergency braking were analyzed, the accuracy of the system model was verified, based on the simulation model. The influences of key parameters on braking process were analyzed, the recommended values for braking system were given, and the influences of key parameters were summarized.