Aiming at the contradiction between the large position tracking error in the traditional backstepping sliding mode position servo system and the contradiction between the dynamic response and the chattering suppression when the fixed sliding mode surface is adopted, a composite control strategy based on disturbance observer and backstepping time-varying sliding mode is designed. Firstly, a state variable is introduced into the traditional exponential reaching law and an adaptive law is designed. A new variable exponential reaching law is proposed to improve the response performance of the system. In order to further improve the convergence speed of the system in each stage, a time-varying sliding mode surface with online optimization is designed by using the idea of ergodic optimization in predictive control, and the stability is proved. Finally, a nonlinear load disturbance observer is designed to estimate and compensate the disturbance of the system. The experimental data show that compared with the traditional backstepping sliding mode control, the steady-state error of the composite control strategy proposed in this paper only accounts for 9/17 of the traditional method, the dynamic response speed is improved by 30 ms, and the antiinterference performance is obviously superior.