Abstract: Aiming at the problem of the shock to the helium turbine expander caused by the AC losses generated during the experimental process of the nuclear fusion device, the finite element method is used to study the time-domain response of the rotor dynamic characteristics under the transient shock. The effects of bearing stiffness, damping and bearing spacing on the vibration displacement of the rotor as well as the self-regulation capability are also investigated. The results show that transient shock causes rotor trajectory disturbances and widens the range of axial motion. The maximum amplitude of the rotor is linearly related to the load. Increasing stiffness can effectively reduce the maximum amplitude of the rotor. Increasing the stiffness, damping and span of the bearings will help to improve the self-adjusting ability of the rotor and make it quickly return to steady state.