On the basis of interior electromagnetism relationship and vector control principle, the vector control system of Permanent Magnet Synchronous Motor (PMSM) without position sensor is designed. There are two main identification methods are introduced to estimate the position and speed of PMSM. One scheme is based on the back Electromotive Force (EMF) and the other is Model Reference Adaptive Standard (MRAS). The former method achieves fast dynamic-state response while the later method obtains better steady-state performance. According to both of them advantages, an improved estimate method which combining the back EMF and the MARS is proposed. Simulation results show that the improved method is feasible and stable.