In order to help piston-type pressure simulator's positioning servo system solve the problem of controllable speed, smooth motion of location approach phase, Sliding Mode Control(SMC) is chosen to design the positioning servo system of permanent magnet synchronous motor(PMSM). A simplified approach was pproposed to design a SMC by analyzing the thoughts and methods of integrated design of position and speed control during existing variable structure servo systems. This approach could achieve speed control and positioning only by switching states of the sliding surface, with characteristics of easy to come true and simple structure. Simulation result verified the correctness of this approach. At last, experimental results show effectiveness and feasibility of design of SMC positioning servo system by pressure simulation experiment in the platform.