The gas-bearing rotor system is studied based on the fluid-structure coupling method.The transient characteristics of the system,such as the dynamic response of rotor displacement under step load and the change of pressure in the gas film flow field,were studied.The results show that under the action of fluid-structure coupling,the rotor finally reaches a stable equilibrium state.Under different step loads,the rotor has eccentric tilt,the rotor end and the tool head have oscillation process.The larger the step load is,the larger the overshoot,rise time and deflection displacement of the rotor are,while the overshoot time becomes smaller.Compared with the steady-state step load,the overshoot of the system under the rectangular step load is reduced due to the preload,and the stabilization time is shortened.The pressure change at the moment of rectangular step load overshoot is small and the fluctuation of the high pressure region is stable,which is beneficial to improve the transient response characteristics of the rotor.