A certain type of servo mechanism′s finite element model was built, then through the analysis of modal experiment, it was found that the servo mechanism′s stiffness was sensitive to the link bearing′s stiffness, meanwhile, the finite element model of the servo mechanism was modified based on the modal experiment′s results. After that, by using modal superposition method, the dynamics response of the servo mechanism under shock environment was analyzed, then by comparing shock experiment, it was verified that the servo mechanism′s finite element model was accurate and effective, finally, by using the modified model, the failure of the servo mechanism′s lead screws was investigated. The proposed method was effective for confirming and simulating the stiffness of the servo mechanism′s link bearing, and had certain instructive significance to analyze dynamics response of this type of servo mechanism under shock environment.