Abstract: Aiming at the harmonic resonance mechanism analysis of multiple LCL-type grid-connected inverters in weak grid,the traditional frequency domain analysis method requires high-order and complex transfer functions to obtain the resonance frequency,and it could not get more resonance information.This paper proposes a modal analysis method to analyze the resonance characteristics of gridconnected system and obtain resonance information such as resonance frequency and node participation factor.First,the Norton equivalent model of a typical three-phase LCL-type grid-connected inverter system is established.Based on this model,the application principles of modal analysis and traditional frequency domain analysis methods are compared,and the advantages of modal analysis method in resonance analysis are illustrated.Second,the modal analysis method is applied to analyze the effects of the number of inverters,inverter type,grid impedance,line impedance,control parameters and LCL parameters on the resonance characteristics of grid-connected system,which is consistent with the results of traditional frequency domain analysis.Then,the modal analysis is used in the resonance characteristic analysis of multiple grid-connected inverters with different parameters.Finally,the correctness of the resonance modal analysis is verified by simulation results.