Abstract: The use of encoders reduces the ruggedness and reliability for the vector control system of permanent magnet synchronous motor; Also, in some cases the mounting of the encoders is a major problem. In theory, speed and rotor position angle of permanent magnet synchronous motor can in real-time be calculated by voltage and current. This paper proposes a sensorless speed control strategy for a permanent magnet synchronous motor（PMSM） based on a new double sliding-mode model reference adaptive system, and the PMSM itself is selected as the reference model and its current model as the adjustable model. Two slide-mode surfaces are formulated according to two models’ output errors. Equivalent current is obtained by sliding mode, and rotor position and speed are achieved by a certain algorithm. The rotor position and speed obtained are used respectively to partake coordinate transformation and speed control in sensorless vector control of PMSM. The simulation research has been done on the basis of theoretical analysis, and shows that the proposed method is effective