For the new control demands of permanent magnet synchronous motor(PMSM) experimental power supply system，speed sensorless vector control method of MW Turbine PMSM was researched, and a new speed estimation method based on model reference adaptive system (MRAS) was proposed. In the method, the q-axis flux error signal was used to construct adaptive rate and estimate the speed. First by Matlab simulation the validity of the method was proved, then the test of two half-direct permanent magnet synchronous generators towed each other was made. The result of the experiment shows that the method has a good speed estimation effect.