A method of reference adaptive control theory (MRAS) to estimate the speed and position of the motor was presented. PMSM as the reference model, the stator current equation with variable speed as the adjustable model. Popov stability theory as a basis to design adaptive rate, when the adjustable model was equivalent to the reference model, speed estimation s equivalent to the true value. The simulation model was built by MATLAB/Simulink, and the simulation results showed that the sensorless control based on MRAS had a good recognition effect.