This paper proposes a control method of synchronous motor without speed sensor based on adaptive extended Kalman filter (EKF). The adaptive EKF observes the stator voltages and currents to estimate the rotor speed and the air-gap flux angle. This adaptive method is applied to adjust the noise mean and covariance to track the dynamic noise, so as to improve the estimation precision. The simulation results show that the adaptive EKF can estimate the speed and the position of air-gap flux accurately and with good static and dynamic performance.