In order to improve the global convergence of sliding mode control (SMC) in speed loop control of permanent magnet synchronous motor (PMSM), a compound sliding mode control strategy is proposed, which combines the characteristics of linear sliding mode surface and non-singular terminal sliding mode surface to form a new sliding mode surface and improve the convergence of SMC in different motion stages. On this basis, the traditional power reaching law is improved to reduce the convergence speed in steady state. At the same time, the disturbance observer based on SMC law is used to observe unmodeled dynamics and unknown disturbance of system, the designed SMC is compensated, the dependence of SMC for high gain controller is reduced. Thus, the chattering of controller in the steady state time due to sliding mode highgain effectively is improved, the control performance of SMC is also improved. Finally, the effectiveness and feasibility of the control method are proved by the simulation and the experiment.