Permanent magnet synchronous motor (PMSM) is a nonlinear system. When the control system operates with external interference, it will obviously affect the operating characteristics of the system, and will also make the torque ripple of the system larger. To solve these problems, the zero voltage vector is introduced to suppress the torque ripple in the traditional control mode. In order to further reduce the torque ripple and speed ripple control process, improve the adaptability and stability of the system, the traditional PI controller is replaced with a Super-twisting sliding mode controller and the function sigmoid(s) in a quasi-sliding mode is used to replace the symbol function sign(s). The torque ripple of the PMSM is studied with MATLAB/Simulink simulation software. The simulation results show that in the traditional direct torque control, the super-twisting sliding mode controller has smaller torque ripple than the PI controller and improves the system robustness.