The nonlinear dynamics of the bidirectional gear-driven friction nanogenerator （TENG） system is modelled by considering the time-varying meshing stiffness， time-varying support stiffness， transmission error， tooth side clearance and bearing clearance. The ode45 function is used to solve the vibration differential equations of system， and the time-varying meshing force diagram， time-frequency diagram， phase diagram， FFT spectrum diagram， Poincaré diagram， bifurcation diagram and three dimensional spectrum diagram of the system are obtained， to explore the effect of the excitation frequency of the external load on the system dynamics characteristics. In addition， friction nano-generation technology is combined to obtain the output performance of TENG under different parameters， and to investigate the mechanism of the influence of external load excitation frequency and average engagement stiffness on the energy harvesting of the system. The results show that the bidirectional gear-driven friction nanogenerator mechanical transmission system has obvious nonlinear characteristics， and reasonable selection of the external load excitation frequency and meshing stiffness to avoid the control of unstable intervals can improve the mechanical energy conversion efficiency and increase the power generation capacity of TENG.