Structured and unstructured uncertainties are the main obstacles in the development of advanced controllers for highaccuracy tracking control of hydraulic servo systems. For structural uncertainties, nonlinear adaptive control can be employed to achieve asymptotic tracking performance. But unstructured uncertainties, such as nonlinear frictions, always exist in hydraulic systems and degrades the tracking accuracy. An incomplete differential backstepping sliding mode controller based on friction compensation was proposed to realize the position control of hydraulic servo systems. The sliding mode control was incorporated into the backstepping design. The problem of structured uncertainties of hydraulic servo system was solved by using the invariance of the control system parameters and external disturbances under sliding mode. The controller was combined with friction compensation to solve the unstructured uncertainty of systems and the incomplete differential was introduced to weaken the differential effect of the controller, to reduce the interference caused by pure differential mutation signal. In addition, the filtering effect caused by incomplete differential could suppress the chattering of the sliding mode control. In the presence of various uncertainties, the asymptotic tracking performance of the system is proved theoretically. The simulation results verify the high precision tracking performance of the proposed control strategy.