It brings great difficulties to select structure and design for automated mechanical transmission shifting actuator, because pneumatic shifting actuator has characteristics of highly-lag response and strong nonlinearity, which leads to big errors when only adopting regular steady-state analysis. Focusing on the features of pressure formed in the chamber of a pneumatic shifting actuator controlled by high-speed on/off valves, a nonlinear mathematical model integrated electricity, magnetism, machinery and fluid power theory was built, which was used to describe the dynamic coupling speciality of the pneumatic shifting actuator. In order to evaluate the accuracy of the model, two indexes including average relative error and maximum relative error were adopted. Compared simulated results with practical ones, the small errors showed that the actuator model was reasonable enough to simulate the dynamic characteristics of pneumatic actuator. Through simulation, several factors, such as volume of pressure chamber controlled by electric valves, the effective areas of electric valve inlet and outlet, were analyzed and they had great influence on the buildup of pressure in the chamber. Finally, the model can be directly used to optimize the structural parameters of pneumatic actuator or to validate some complex control algorithms, which is a good platform to solve shifting force control problem during pneumatic shifting process. However, the nonlinear equations of the system are so complex that they will not be able to calculate on a real-time platform unless they are simplified. The further work is to simplify the complex model into a simple one, which will not reduce the dynamic characteristics sharply and can be run on a real-time platform such as DSpace.