Aiming at the problems of poor accuracy, slow convergence rate and high jitter of traditional super-twisting sliding mode observer, a permanent magnet synchronous motor(PMSM) speed observation technique based on the improved super-twisting algorithm was proposed. Firstly, a segmented exponential function was used to replace the switching function to eliminate the phase delay problem due to the low-pass filter, and the adaptive sliding mode gain was designed to achieve stable tracking at different speeds. Then, in order to solve the problem that the traditional quadrature phase-locked loop failed when the motor steering was changed, an improved quadrature phase-locked loop was proposed, so that its output was independent of the rotation direction, so as to realized the correct tracking of the forward and reverse rotation. Finally, due to the wrong convergence point of the proposed improved quadrature phase locked loop, there was a 180° phase difference between the estimated position and the actual position, an adjustment function was designed to solve this problem. The simulation results show that compared with the traditional sliding mode observer, the proposed improvement method has faster response and better dynamic performance.