In the process of rotor position estimation of PMSM based on single-frequency pulse voltage injection method, there are some problems, such as incomplete removal of dc component, easy influence of inductance, when using filter method and direct calculation method to eliminate dc component. A synchronous modulation technology is proposed to remove the dc component. This rotating voltage vector is injected into stationary coordinate system, and using band-pass filter response to high frequency current is extracted, and then use the synchronization modulation technology to achieve four independent rotor position information, and cancel by poor response to the current of dc component, and finally using two-phase type phase-locked loop to get the final estimate rotor position. The simulation results show that compared with the filter method and the direct calculation method, the proposed method reduces the maximum error of rotor position estimation by 0.1rad and 0.14rad respectively when the motor starts. The position estimation error of the proposed method is minimum under the condition of inductance variation. It is proved that the proposed method has the advantages of high precision and insensitive to inductance change.