For the inaccurate speed estimation in speed sensorless servo system which is caused by the uncertainty of the stator resistance, an improved model reference adaptive system (MRAS) method is proposed in this paper. In this method, the current model of PMSM is regarded as adjustable model. Moreover MRAS’ adaptive laws which add resistance estimation are designed. And then a simplified model is achieved according to the control strategy. Finally the simulation model is built under the Matlab/Simulink. The result shows that the speed estimation with resistance estimation has strong robustness in the effect of the uncertainty of the stator resistance in a wide range of speeds.