In order to study the stability of the slit throttle air bearing-rotor system under step load,combining the hydrodynamic with rotor dynamics equations,fully comsidering the nonlinear motion of the rotor under the action of the flow field,the dynamic mesh technique was used to establish the bearing-rotor dynamic coupling calculation model.The fluid-solid coupling method was used to obtain the axial trajectory and the flow field distribution in transient and steady state.The axial trajectory and the distribution of the flow field inside the bearing were obtained through the analysis and calculation,and the stability of the system was analyzed by introducing the time domain parameters.By changing the structural parameters of the air bearing,the influence of different bearing parameters on the rapidity and stability of the system in the transient phase at a specific speed were studied.The results show that the dynamic stability of the system can be improved by controlling the slit spacing,depth and width of the bearings.