Abstract:As the gear transmission system with clearance responses in a way of abundant nonlinear dynamics, this paper establishes a dynamic model of twodegreeoffreedom gear transmission system. Firstly, the bifurcation of the gear transmission system and the chaotic dynamic behavior using the numerical method is investigated, and the nonsmooth function is then fitted with the smooth function. Moreover, nonlinear dynamic phenomenon of gear transmission system with fitted clearance function is achieved using multiscale perturbation. Eventually, the results are compared with that of nonsmooth system without numerical fitting, which also provides essential data for the future research of gear transmission system with a clearance.