Abstract: In a high proportion of renewal energy power systems, the dynamic interaction between grid-connected inverters and the power grid makes the problem of harmonic resonance in the system increasingly complex. To effectively evaluate the harmonic resonance of the system, this paper proposes a method for evaluating the resonance strength of a multi-inverter grid-connected system and identifying the impedance of its key nodes. Firstly, based on the equivalent RLC parallel circuit with modal impedance, a quality factor index is defined to characterize the damping characteristics of resonant modes. The quality factors of each resonant mode are calculated using the Nyquist plot, and the resonance strength of the multi-inverter grid-connected system is evaluated by analyzing their numerical values and positivity and negativity. Then, the relationship between modal impedance and node impedance is derived, and a participation factor index is defined to characterize the excitability and observability of the resonant mode at the corresponding node impedance. The key nodes where resonance occurs are identified by comparing the participation factors of the resonant mode on the impedance of each node. Finally, the numerical results validate the correctness and effectiveness of the proposed method.