The cutting force suffered by the machine tool in the cutting process can be assumed to be the combined force of the steady state force and the dynamic disturbing force.In order to investigate the dynamic characteristics of electric spindle system supported by gas bearings,sine wave was used as dynamic disturbance loading form,and the dynamic characteristics of a simplified model of a gas bearing rotor system were studied by combining the harmonic excitation method with the bidirectional fluid-structure coupling numerical simulation.The dynamic stiffness and damping coefficients were identified.Through modal analysis,the system vibration modes and natural frequencies of the rotor under different steady-state forces were obtained.The results show that with the increase of steady-state force,the growth rate of Kyy of the lower radial bearing is greater than that of Kxx,while the cross stiffness and cross damping are almost unchanged.The main stiffness of the lower radial bearing is greater than the cross stiffness,and the main damping is greater than the cross damping.When the steady-state force ranges from 50 N to 200 N,the y-shift at the lower end of the rotor first increases and then decreases with the increase of dynamic disturbance frequency.The resonance frequency of the system increases with the increase of the steady-state force.