Abstract: In a distributed generation system, the stability of grid-connected inverters that are used as the dominant power interface device is directly related to the reliable operation of the grid-connected system. The impedance-based analysis method can be employed to effectively study the interaction stability between grid-connected inverters and grids, so the impedance modeling of grid-connected inverters is the important premise for the analysis of impedance stability. Based on the application of three-phase LCL-type grid-connected inverters, the harmonic linearization method was adopted to analyze the frequency characteristic of the phase-locked loop（PLL）, and a parameter design approach of PLL regulator was proposed in this paper. Meanwhile, the impacts of the factors that include PLL and digital control delay on the impedance characteristic were considered, and the positive-sequence and negative-sequence impedance models of the three-phase LCL-type grid-connected inverter was built by combining harmonic linearization and symmetrical component methods. Finally, the frequency characteristic of PLL and the output impedance model of the three-phase LCL-type grid-connected inverter were verified respectively by the simulation and experimental results, which effectively proved the correctness of the theoretical analysis.