The sensorless vector control system of permanent magnet synchronous motor (PMSM) is a system with uncertainty and external disturbance. According to sliding mode control theory, this paper realized robust control of the uncertainty and external interference by use of the equivalent control matched with switching control. Meanwhile, in order to eliminate the adverse effect produced by the chattering of the sliding mode, this paper adopts the saturation function of quasi-sliding mode instead of the traditional sign function. Furthermore, the exponential reaching law is used to further weaken the chattering and to ensure the rapidity of the system. Simulation and experimentation show that this control method has good dynamic and static performance.