Aiming at the problem that traditional fullorder flux observer led to the inaccuracy of the flux linkage and even the instability of the system under internal and external disturbances, the influences of the observer pole distribution and the internal or external disturbances were analyzed. Then the feedback gain matrix coefficient was designed, and a robust adaptive state observer was proposed to estimate the flux linkage. When the system was influenced by the internal or external disturbances, in order to maintain the system’s good dynamic and static performance, the feedback gain coefficient was automatically reduced while maintaining the stability of the system. The flux estimation accuracy, speed fluctuation and torque ripple under internal and external disturbances were compared between the robust adaptive state observer and traditional fullorder flux observer. Simulation and experimental results showed that the robust adaptive state observer had better antijamming performance than traditional fullorder flux observer.