The gear backlash and bearing clearance have a significant influence on the nonlinear dynamics of gear system. Firstly, a nonlinear dynamic model of gear pair system with multi-clearance is established, considering comprehensively time-varying meshing stiffness,static transmission error, gear backlash and bearing clearance. Then, the dimensionless dynamic equations are derived. Finally, the equations are solved by using numerical integration method. And the bifurcation features of the system are analyzed with different parameters including gear backlash, bearing clearance and damping coefficient under different loaded conditions. The results show that when gear backlash changes, the system undergoes rich motion forms consisting of period-one, period-doubling and chaos under lightly loaded condition. However, the dynamic characteristic of the system is not changed under heavily loaded condition, while only the vibration amplitude changes. Similarly, the motion state of gear system does not change when bearing clearance increases under heavily loaded condition, whereas the system will enter into complex motion states under lightly loaded condition with the change of bearing clearance. The research results provide certain guiding role for reasonably choosing and optimizing backlash value of gear system.