In this paper, the second order sliding mode control law was designed based on the super-twisting algorithm and the switching function sign(s) was replaced by the saturation function sat(s) for the torque and flux controller in the permanent magnet synchronous motor double closed loop control system. The stability of the system was proved by Lyapunov function. The traditional direct torque control method and the simulation results of this method were analyzed by using MATLAB / SIMULINK simulation tools. The results show that the torque ripple based on the direct torque control system of the super-twisting algorithm is reduced by 4 times compared with the traditional direct torque ripple. Speed response time is shorter. Speed fluctuation is smaller. System stability has improved significantly.