In order to research the influence of suspension types of linear induction motor (LIM) on the dynamics performance of vehicle system, and further decrease the air gap fluctuation of LIM and reduce wheel-rail impact by using active suspension, the multi-body dynamics model of metro vehicle was set up. The electromagnetic force model of LIM was built by using classical electromagnetic theory. The model of constant air gap control system with electromechanical actuator was established. The constant air gap control strategy and its influence on the vehicle's dynamics were studied by numerical simulation. Simulation result shows that the air gap change is mainly caused by the change of load when large-deflection primary suspension and LIM frame suspension are adopted, its frequency is very low, so the constant air gap control of LIM is easy to carry out. The control can guarantee that the vehicle meets the requirement of air gap under different load conditions, vertical wheel-rail interaction force reduces by about 10 kN, and the comfort index decreases by about 0.1. Moreover, the dynamics performance of the vehicle will be improved compared with traditional LIM vehicle, and its traction force is smoother.