A zero phase shift synchronous rotary frame filter-based single-phase locked loop is proposed to overcome the harmonic ripple in the rotor position estimation of sliding mode observer and the phase lag caused by the first stage low-pass filter. Firstly， the sliding mode observer is established based on the mathematical model of the motor， and the reason for the phase lag of the traditional synchronous rotary frame filter is analyzed； Secondly， the first stage low-pass filter is omitted， and the high-order harmonics and chattering in back electromotive force are filtered by dq transformation； Finally， the Matlab/Simulink simulation model and the sensorless vector control experimental platform of permanent magnet synchronous motor are built to compare the performance of the traditional synchronous rotary filter and the zero phase shift synchronous rotary frame filter based on single-phase locked loop. Simulation and experimental results show that the proposed method has better tracking performance and higher observation accuracy than the traditional synchronous rotary frame filter structure.