In the speed control system of permanent magnet synchronous motor (PMSM), PI controller could not meet the requirements of high precision control. A sliding mode variable structure control method based on a new reaching law is proposed. The new reaching law combined the advantages of exponential reaching law and power reaching law, and with the addition of system state variables, it could effectively suppress the chattering of sliding mode controller in the sliding stage. The constant velocity approaching term was related to the sliding surface switching function, which ensured the effective and steady approaching of the reaching law near s=0 and weakened chattering; the exponential approaching term was associated with the system state variable x1 to increase the approaching speed. The stability of the proposed method was proved by using the Lyapunov stability theory. The speed controller based on the new sliding mode algorithm was compared with the PI speed controller and the traditional sliding mode controller by simulation. The simulation results under the noload start, sudden load and variable motion conditions showed that the system using this controller could achieve rapid response, high stability and strong resistance to load disturbance.