In order to study the influence on dynamic performance of metro vehicle during the air loss of air spring, the nonlinear dynamic model of metro vehicles and the stick-slip contact force model of air spring in the state of air loss were established. And the critical speed, derailment coefficient, lateral wheelset force，wheel rail lateral force，wheel unloading rate and Sperling value of the metro vehicle in the normal state of the air springs and the air loss of the whole vehicle air spring were calculated and compared. The results show that the critical speed of the metro vehicle is reduced, and the derailment coefficient, the wheel unloading rate, the lateral wheelset force and wheel rail lateral force, and the lateral and vertical Sperling value of the metro vehicle in- creases obviously when air spring loses air. Since the derailment coefficient and vertical Sperling value are af- fected significantly, the state of the air spring deserves more attention to ensure the smooth and safe operation of the metro vehicle.