Abstract: The grid voltage synchronization method is one of the key technologies of distributed power supply microgrid. The accuracy of obtaining phase angle directly affects the control performance of grid side converter, especially in vector control system. Background with power grid harmonic, this paper analyses the phase lock error of the grid voltage harmonic by establishing the mathematical model of the grid voltage harmonics, and proposes an improved second-order integrator phase-locked loop method based on the internal model of repetitive control, the internal model is embedded in the DSOGI-PLL, in the fundamental frequency and the harmonic frequency generate resonant gain, through the 50Hz wave trap, the harmonic component is separated, and the fundamental phase angle can be accurately locked. Finally, the simulation and comparison of several traditional phase-locked methods are carried out to verify the effectiveness and feasibility of the proposed method.