In view of the overshoot of speed control system in excessive dynamic speed change and dynamic loading in the traditional sliding mode observer in permanent magnet synchronous motor (PMSM), as well as a large jitter generated in the estimation of counter electromotive force, a proposal has thus been made of a self-tuning speed control method of permanent magnet synchronous motor based on the sliding mode observer. Firstly, the Sigmoid function is used to replace the constant switching function, with the inverse EMF estimated by the sliding mode observer. Then, the rotor position and velocity signals are to be extracted from the estimated counter electromotive force by using the phase-locked loop. Finally, a comparison is to be made between the observed velocity value and the given value, thus realizing the parameter self-tuning by fuzzy PI. The simulation results show that, compared with traditional sliding mode observer method, this method helps to eliminate the jitter, thus greatly improving its tracking and robustness.