A speed sensorless vector control system was established based on the fundamental equation of vector control of asynchronous motor. The theory of model referencing adaptive control was applied to the system rotor-speed-estimation and the adaptive institutions were modified by way of segmented variable parameters in order to improve the estimation speed and accuracy; The adaptive fuzzy PI control was brought in speed regulator to improve the reliability and robustness of asynchronous motor. Simulation results showed that the system had a better dynamic performance and tracked the variation of the motor speed accurately, and it had strong robustness and stability.