[Objective] To address the contradiction between reaching speed and chattering suppression in the traditional sliding mode controller for surface-mounted permanent magnet synchronous motors (SPMSM), this study proposes a sliding mode control method based on improved variable-speed double-power reaching law. [Methods] First, based on an improved variable-speed double-power reaching law, sliding mode variables and system variables were introduced in addition to the traditional double-power reaching law, making the reaching law exhibit variable-speed characteristics. The hyperbolic tangent function was employed in place of the sign function to suppress chattering, and the stability of the proposed speed controller was proven using the Lyapunov theorem. Next, to address the impact of load disturbances on system performance, a non-singular fast terminal sliding mode observer was designed. This observer integrated a non-singular fast terminal sliding mode surface with a high-order sliding mode control law, which could not only suppress system chattering but also provide real-time disturbance compensation. This improved the accuracy of disturbance estimation in the speed control system and reduced system chattering. Finally, simulations based on Matlab/Simulink were conducted, and a motor experimental platform was established to compare the proposed method with traditional sliding mode control and other variable-speed sliding mode control methods. [Results] Simulation and experimental results show that the SPMSM sliding mode speed control method based on the improved variable-speed double-power reaching law can suppress system overshoot, enhance system response speed, and provide real-time compensation in the presence of disturbances. [Conclusion] The results demonstrate that the proposed control method enhances the dynamic performance and robustness of the system.