There is a complex relationship between reaching speed and chattering in exponential reaching law of sliding mode control for permanent magnet synchronous motor (PMSM). Based on fast power reaching law, a new reaching law with adaptive adjustment of power coefficient is proposed. The proposed reaching law introduces the system state into the coefficient of power term, and the effect of adding power term in the reaching process of the system state from far to near the sliding surface is realized. On the premise of guaranteeing the characteristics of power term, the convergence speed of the dynamic response process is greatly improved. The load torque is a disturbance term in the sliding mode speed controller. A sliding mode observer with power term is designed, and the observed value is used as the torque feedforward compensation. The simulation results show that: compared with the fast power law, the proposed reaching law has faster convergence speed, and the load observer can accurately track the change of load and improve robustness of the system.