Abstract: The traditional linear control theory can not meet the system requirement of a permanent synchronous motor (PMSM) for its motion control is a coupling and nonlinear control system and measurement noise also exists in the control system. A method to estimate the rotor position of PMSM was presented based on fluctuating high-frequency voltage signal injection and Kalman rotor-position-estimator. When a fluctuating high-frequency voltage signal was injected into stator winding, the corresponding current signal containing the information of rotor position was demodulated and delivered into the Kalman rotor-position-estimator. Then the rotor position would be detected accurately. Simulation results verified the method can track the rotor position accurately, even though system noise and measurement noise exist in the control system.