In the rotor field oriented vector control system, the use of permanent magnet synchronous motor voltage equations and flux equations derived PMSM position and speed estimation method has its unique advantages, The advantage of this approach is to calculate a simple, fast dynamic response, and easy to implement. However, when permanent magnet synchronous motor running at low speed, back EMF would be very small, which can not guarantee the accuracy of estimates. In addition, the position and speed estimation parameters of permanent magnet synchronous motor is largely in dependence on the running status of permanent magnet synchronous motor ,and vulnerable to temperature and magnetic saturation phenomena.All of these elements will lead to error increase. In order to solve the problem of inaccuracy in parameters estimation of motors at low speed, PI controller is introduced to obtain the rotor speed information, and then make up for deficiencies in the estimation algorithm. At the same time, this method can be applied to achieve smooth switching of high speed switching of the motor.