Abstract: Impedance-based method is widely applied to analyze the stability of grid-inverter interconnected system. In impedance modeling, it is assumed that a three-phase interconnected system can be decoupled into a positive-and a negative-sequence subsystem, and each subsystem has the single-in-single-out characteristic in the frequency domain.However, if there is frequency coupling in the system, the positive-and negative-sequence impedance models are no longer decoupled, and the original stability analysis method is no longer applicable. In this paper, the frequency coupling characteristic of grid-connected inverter was studied, and an analytical model with considerations of multiple causes to frequency coupling was modeled and validated. Based on this derived model, the influencing factors of frequency coupling were analyzed, and the system stability was also analyzed.