Based on the equivalent Norton model of large-scale photovoltaic (LSPV) plants, the coupling among inverters in LSPV plant and between LSPV plant and the grid are studied through impedance analysis. The study reveals the harmonic mechanism that coupling between grid impedance and equivalent admittance of inverter will amplify harmonics in the system. To remove the amplification to harmonics, the strategy of adding a virtual admittance to filter harmonics is proposed. The strategy is realized to improve inverter admittance by the voltage at the point of common coupling (PCC) feedback through the combination of a first-order process and a second-order notch filter. The system with the proposed strategy owns characteristics of making harmonic current through the virtual admittance and fundamental frequency current blocked. In the end, the result of simulation and experiment validates theoretical analysis.