Objective To address the inherent conflict between reaching speed and system chattering in permanent magnet synchronous motor PMSM control systems this paper proposes a composite control strategy. This strategy integrates a sliding mode speed controller based on an improved variable-speed double-power reaching law with a disturbance observer. Methods First the sigmoid function was introduced to replace the sign function. This replacement smoothed the control signal and effectively reduced chattering. Second system state variables were incorporated into the power terms to establish dynamic correlations resulting in the development of an improved variable-speed double-power reaching law. This enhancement enabled the sliding mode speed controller to achieve a faster reaching speed. Finally to address the issue that sliding mode control typically requires a high switching gain to handle disturbances a disturbance observer was designed to observe and compensate for system disturbances in real time. Results Simulation results showed that compared with traditional methods the system under the proposed control achieved 0 overshoot. The settling time of speed and the settling time of torque were both reduced by at least 0. 01 s and the three-phase currents recovered rapidly with smooth waveforms after a sudden load change. Conclusion The improved variable-speed double-power reaching law achieves a fast overshoot-free response during transient states and shortens the settling time under sudden load changes. In the steady state it exhibits strong resistance to load torque disturbances and effectively weakens chattering.