Abstract: Since high chattering and phase delay of traditional control strategy cannot be solved with the sliding mode controller and sliding mode observer, a sensorless control strategy is proposed to improve SPWM sliding mode. First, the third harmonic is added to the SPWM voltage modulation method, which is rarely used and easy to implement in engineering, so as to improve the DC voltage utilization of the inverter. Second, choose new gradient approach rate, rather than improved speed sliding form controller. And then, design an adaptive Super-Twisting sliding mode observer which observes the rotor angle and speed. Finally, compare the proposed strategy with the traditional velocity PI & sliding mode observer and the traditional velocity sliding mode & sliding mode observer strategies through simulation. And compared to the two traditional strategies, the proposed strategy brings decreases on response time (by 0.025 s and 0.004 s), chattering (by 60.71% and 16.98%),the observer solves the phase delay problem well and reduces the speed chattering and angle estimation error .