To overcome the problems of multi motor differential out-of-step oscillation and poor synchronization stability, a multi-PMSM synchronous control method based on a new adaptive integral sliding mode and disturbance observation is proposed. First, an improved bias-coupled synchronous control structure is constructed. Then, a PMSM controller based on a new adaptive integral sliding mode control (NAISMC) is designed. The sliding mode disturbance observer (SMDO) is used to observe the motor load disturbance, and is combined with an improved deviation coupling synchronous control structure. An improved multi-PMSM deviation coupling synchronous control method based on NAISMC and SMDO is proposed. Finally, experimental analysis is done. The results show that the synchronous control method proposed in this paper can effectively ensure that the four motors have good synchronization performance, improves their anti-disturbance ability, and ensures the stability of multi-motor synchronization. This work is supported by the National Natural Science Foundation of China (No. 51605003 and No. 51575001).