Abstract: In vector control system of asynchronous motor, control performance is often influenced by accuracy of estimated flux value. On the basis of analysis for flux observer based on low-pass filter, the paper put forward a control scheme of model reference self-adaptive used to estimate resistance of stator and rotor and rotate speed of motor, and designed a novel self-adaptive stator flux observer based on Popov's inequality. The observer can accurately obtain estimated values of stator resistance and rotate speed, and distinctly improve its performance. The simulation result verified advantages of the observer.