Because of the mismatched disturbance and uncertain parameter changes, electro-hydraulic position servo system has some problems such as chattering and poor tracking control performance. In view of the nonlinearity of electro-hydraulic position control, a high order nonlinear sliding mode variable structure control based on the backstepping method is proposed, which ensures the robustness to the mismatched disturbance and the uncertain parameters. Using the impulse function to replace the symbol function, the chattering of the system is reduced. Finally, the robust sliding mode observer is added to the closed-loop control system to estimate the unmeasured state and achieve output feedback control. The unit step response is simulated by first order sliding mode control and nonlinear high order sliding mode control. The results show that the control method proposed in this paper has the stability and convergence of reference position for zero steady-state error, and realizes electro-hydraulic servo position tracking.