A current adaptive sliding mode control method based on a disturbance observer was proposed in consideration of the influence of disturbance on the performance of speed servo system in a Permanent Magnet Synchronous Motor(PMSM). An adaptive law was derived to estimate the internal parameter variations and to compensate the disturbance of the model uncertainty. Then, a Sliding Mode Disturbance Observer (SDOB)was designed to estimate the external load disturbance in real time. The estimated values were designed as a feed-forward to compensate the current adaptive sliding mode controller and to further increase the resist-disturbance capacity of the system. The experimental results demonstrate that the system based on the current adaptive sliding mode control and disturbance observer could track the speed command of 900 r/min rapidly and accurately without overshoot, the regulation time is 0.08 s, and the steady-state accuracy is ±5 r/min. When a 0.6 N·m load torque disturbance is added, the method based on current adaptive sliding mode control and disturbance observer gives a maximum speed fluctuation of 21 r/min. As compared with PI control, the speed fluctuation is reduced by 3.4%. The simulation and experimental results indicate that the proposed control method improves the dynamic response and robust performance of the speed servo system and alleviate the chattering of sliding mode control system effectively.