Abstract: To suppress the increasingly complex grid background harmonics in the new power system under the“Dual High”background,the grid-connected system usually needs to add the PCC node voltage feedforward control strategy on top of the existing control scheme. However,existing studies have shown that due to the interplay between the inverter and the grid impedance under weak grid this strategy would reduce the passivity of the equivalent output impedance of the gridconnected inverter in the middle and low frequency band,which is easy to cause the broadband resonance of the grid-connected system. To address this issue,firstly,the advantages and inherent defects of the traditional PCC node voltage feedforward strategy in suppressing grid background harmonics are analyzed by establishing the equivalent output impedance model of the grid-connected inverter system under weak grid,and on this basis,a new network-side active damping strategy is proposed based on the theory of passivity,which not only realizes the full passive equivalent output impedance of the grid-connected inverter system in a wide frequency range by adding active compensation device in the capacitor branch and the additional control strategy of the main inverter, but also effectively represses the grid harmonics disturbance and greatly enhances the adaptability of the system under weak grid. Finally,the validity of the control strategy is proved by building the system emulation model when the grid-connected inverter is connected to a weak grid.