Abstract: To improve steady-state and dynamic performance of sensorless control of permanent magnet synchronous motor with medium and high speed, and solve the problem that traditional quadrature phase-locked loop can not operate effectively when the motor is reversed, a sensorless control strategy of interior permanent magnet synchronous motor based on super-twisting sliding-mode observer and improved quadrature phase-locked loop was proposed. In the two-phase stationary coordinate system, the super-twisting function is used to replace switching function of the traditional sliding-mode observer to establish super-twisting sliding-mode observer, which can fully suppress chattering of sliding-mode and avoid using low pass filter, and can solve problems of phase delay and amplitude attenuation caused by low pass filter. The improved quadrature phase-locked loop algorithm avoids use of tangent function and uses a simple reverse electromotive force signal reconstruction strategy to obtain the error signal. Compared with the quadrature phase-locked loop algorithm based on tangent function, the improved algorithm is more simple and effective, and can make the motor reverse operation. In addition, the speed and position estimation error is small in operation process.The simulation results verify reliability and effectiveness of the control strategy.