Abstract: A finite element simulation of a servo transmission system is accomplished based on LS-DYNA.The torsional-vibration dynamic response of the gear-transmission servo system,which could be helpful to the design of servo transmission system,has been obtained by proposing central difference algorithm as the core arithmetic for time-frequency analysis.Taking into consideration the nonlinear factors such as the contact between gear pairs,bearing pairs,as well as the one related to the gear box,higher accuracy in the dynamic responses computation can be achieved.