In order to solve the problem of stator flux linkage and electromagnetic torque found in traditional direct torque control system, a control scheme based on sliding mode variable structure has thus been proposed. With SVPWM space voltage vector pulse width modulation adopted to replace hysteresis control and switch table, the second-order sliding mode controller of torque and flux linkage is used to replace traditional PI regulator, thus enhancing the control precision of torque and flux linkage and restraining its buffeting. The utilization of the sliding mode observer instead of the sensor helps to improve the control performance and anti-interference ability of speed control system. Matlab simulation results show that the improved control system can effectively reduce the flux linkage and torque ripple, improve its static and dynamic performance and robustness of the system as well.