Abstract: The initial position detection technology of surface mounted permanent magnet synchronous motor (SPMSM) is studied by using high frequency square wave signal injection method. Firstly, the high frequency square wave signal injection method and the magnetic pole discrimination technique are theoretically analyzed and the formula is deduced to obtain the expression of the initial position of the rotor. Then, the vector control system and the initial position detection system of permanent magnet synchronous motor (PMSM) are built by Matlab/Simulink. The simulation results show that the method can accurately obtain the initial position information of the rotor with an error of 0.05 rad. Finally, the program of initial position detection and pole polarity identification is written, and the hardware experiment is carried out on the motor platform. The experimental results show that the method can accurately obtain the initial position information of the rotor, and the error is 0.018 rad.