Abstract: A mathematical model of induction motor was constructed. A new speed identification method of model reference adaptive system based on improved back-EMF was proposed on basis of analysis of stability of the model reference adaptive system based on reactive power. Error signal of speed identification of model reference adaptive system was re-constructed by the method. The error signal was composed of cross and dot product of the back-EMF error vector and the rotor flux vector. The rotor speed of the motor was identified by the error signal. The experimental results show that the new method is effective to solve problem of instability of the model referencing adaptive system under status of motor parking brake and power generation.