In the surface-mounted permanent magnet synchronous motor speed control system, the problems of large overshoot, poor robustness and susceptibility to load disturbance in classic PI control are addressed. A controller based on the second-order sliding mode algorithm was designed. The integral sliding mode surface was adopted. The convergence in finite time was proved by Lyapunov function, and it was applied to the speed control. It is insensitive to the change of internal parameters Aiming at the problem of load disturbance, a load torque observer was designed to compensate the observed value of the load torque into the current to reduce the influence of the load disturbance on the system. Simulation and experimental results show that the control method improves the speed regulation system of the permanent magnet synchronous motor significantly, can respond quickly to a given speed without overshoot, and it has strong robustness