Poor robustness and slower torque recovery of sudden load torque occur in permanent magnet synchronous motor (PMSM) speed control system using PI control algorithm and exponential sliding mode control (SMC) algorithm. In order to solve these problems, an improved reaching law SMC algorithm is designed, which is used in the speed controller of the PMSM speed control system. In order to verify the feasibility of the proposed SMC algorithm, MATLAB/Simulink is used to simulate the PMSM double-closedloop speed control system, and the traditional exponential reaching law SMC algorithm and PI control algorithm are compared. The results show that the improved reaching law sliding mode speed controller has better robustness and resistance to load disturbance.