In order to ensure the quality of electric energy, the current with harmonic component generated from inverter should meet the requirements of interconnection standard. A method based on impedance analysis, which focuses on the problem of harmonic interactions between the grid with background harmonic and PV grid-connected inverters, is presented in this article. Owning to the intersection between the effective output impedance of inverter and the equivalent grid impedance at the point of connection(POC), the amplitude of grid-connected current increases significantly, which leads to the harmonic resonance phenomenon. This paper not only establishes a Norton equivalent model of inverter but also deduces the expression of the inverter equivalent output impedance, and what’s more, analyzes the reasonable value range of the equivalent output impedance of inverter on basis of the maximum limit value of harmonic voltage and current, and also on basis of the conditions of harmonics. Two different kinds of control strategies(PI and quasi-PR control) are given out in this article to regulate the equivalent output impedance of inverter, which is used to restrain the harmonics effectively. The simulation results have proved the effectiveness of such control methods.