Abstract: With the rapid development of renewable energy sources, the number of inverter grid-connected installations continues to increase, leading to increasingly complex harmonic resonance characteristics of multi-inverter grid systems. Serious harmonic resonance accidents will occur when the excitation frequency of harmonic sources matches the system’s resonant frequency. To comprehensively grasp the harmonic resonance characteristics of multi-inverter grid systems, in this paper we first establish the corresponding equivalent Norton circuit model based on the structure of a single inverter grid system and the inverter control diagram. Then, the model is extended to obtain an equivalent model for multi-inverter grid systems. A comprehensive resonance assessment method is proposed, utilizing modal analysis to determine the resonance conditions of the grid-connected system. Furthermore, the participation degree of inverter nodes, transmission line nodes, and common connection points in resonance is determined using the participation factor method. The impact of various inverter parameters on resonance is further investigated by analyzing the impedance and frequency influence indicators. A three-inverter grid system is utilized as a case study for harmonic resonance assessment. Finally, the proposed harmonic resonance assessment method is validated through simulation, providing a basis for inverter parameter design and system resonance control.