Abstract: In the drive system of permanent magnet synchronous motor(PMSM) controlled by inner-loop field orientation control(FOC) and outer-loop classical proportional integral(PI), it is prone to appear uncertain defects such as low detection accuracy of external disturbance, chattering and large overshoot of speed loop. In order to solve the chattering problem of PI control and improve the anti-interference ability of the system, an integral super twisting sliding mode controller(ISTSMC) is proposed. In order to realize sensorless control and online estimation of motor speed and position, the sliding mode observer based on extended Kalman filter(EKF) is also designed，and a piecewise sinusoidal function is designed to replace the traditional sgn function based sliding mode observer to reduce chattering. In Matlab/Simulink simulation, the speed response and detection accuracy of the system under various fault disturbances, reverse operation and load disturbances are analyzed. The results prove the feasibility and superior dynamic performance of the proposed system.