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Aiming at the inherent buffeting problem in the observer, hyperbolic tangent function with variable slope is selected as the switching function to weaken the chattering of the switching surface, and a fuzzy controller is designed to dynamically adjust the slopes of the switching function according to size of system buffeting for changing the thickness of the boundary layer, which well balances the contradiction between the buffeting and the steady- st ate error. Furthermore, a fixed sliding mode gain is easy to cause large buffeting at low speed and inaccurate estimation of position and speed at high speed. Under the condition that the observer satisfies Lyapunov stability, the sliding mode gain based on the adaptive adjustment of rotor angular speed is designed, using PLL technology to extract the rotor position and speed information improves the estimation accuracy and weakens the computational noise. The simulation and experimental results show that the improved sliding mode observer has high estimation accuracy and small buffeting, and the observation effect is still good in the wide speed range of the PMSM control system. [ABSTRACT FROM AUTHOR]