According to the self-excitation doubly salient retarder’s braking torque equation and dynamic equation, its braking torque model and the vehicle’s dynamics model can be built using Matlab/Simulink. The simulation results show that the relationship of automobile braking torque, excitation current and retarder speed, and that the variation of vehicle deceleration rate. This method can optimize the control system of retarder, as well as can be used as auxiliary means of verification of doubly salient self-excited retarder design.