Position servo system of valve-controlled hydraulic steering gear is an important branch of hydraulic field. Because of the internal leakage of the valve and the uncertainties in the working environment, it is a typical nonlinear control system. Therefore,it is one of the typical objects of control technology. The traditional PID controller can’t meet the requirements of control accuracy and speed. In view of this, this paper will carry out the algorithm research of Sliding mode variable structure control, apply it to the valve-controlled hydraulic servo system, and use the simulation results to analyze the feasibility and effectiveness of the control strategy.