In the vector control system of permanent magnet synchronous motor (PMSM), aiming at the problems of insufficient control accuracy, large overshoot and easy to be affected by external disturbance of the traditional PI controller, an inverse sliding mode controller is proposed to replace the traditional PI controller. The inverse sliding mode controller is produced by the combination of inversion method and sliding mode control theory, In the design of reaching law, hyperbolic tangent function and system state variables are introduced to form a new reaching law, which replaces the traditional exponential reaching law, improves the convergence speed of the system and reduces the chattering phenomenon of sliding mode. The simulation model is built in MATLAB/Simulink. The simulation results show that this method makes the system have a good control effect on the motor speed. Compared with PI control, traditional sliding mode control and variable exponential sliding mode control, it has better dynamic response performance, the overshoot is reduced by 22.15%, 18% and 2.75% respectively. The anti-disturbance ability of the system is improved and the system has strong stability.