Auxiliary bearing is mainly used to support the dropping rotor with high revolution when the active magnetic bearing fails to work,which must be able to bear the huge impact load.In order to reduce the impact force to the auxiliary bearing effectively and protect the active magnetic bearing and rotor system,a new auxiliary bearing structure based on axial buffer shim was proposed.Based on the finite element method and LSDYNA software,combining with the experiment rig of the active magnetic bearing in the helium circulator of 10 MW high temperature gascooled reactor (HTR10),the structure characteristic and stress state were analyzed for the auxiliary bearings with and without axial buffer shim on the bearing outer ring when rotor drops.The stress distribution of the axial buffer shim was also analyzed,and the reliability of the auxiliary bearing when rotor drops is verified theoretically.The result shows that the buffer shim can effectively reduce the impact of the rotor drop to the auxiliary bearing,which provides an important reference for the rotor drop experiment and theoretical foundation for the practical application of the structure.