Based on the mathematical and physical equations of thermodynamics and fluid mechanics theories, the bellow-fixed orificeauxiliary tank model and the bellow-pipe-auxiliary tank model of air spring were established respectively. With Matlab/Simulink, the influences of the pipe length, the orifice diameter and the auxiliary tank volume on the dynamic characteristics of air springs were analyzed. The simulation results showed that: when the pipe was long, the inertia of the air mass in the pipe must be taken into account, but the short pipe could be equivalent to the fixed throttle; dynamic vertical stiffness of air springs tended to constant level in the low and high frequency respectively; there was a defect of the fixed throttle for that open too large in low frequency and too small in high frequency; Both the fixed throttle diameter and the auxiliary tank volume had great influences on the damping characteristic of air springs.