In order to analyze the mechanism of harmonic resonance phenomenon in PV grid-connected system, a LCL type inverter model is established, which adopts frequency domain analysis to research harmonic resonance problems when multiple inverters are connected to the grid. Besides, the inverter output impedance model of a single and multiple inverters is established to study the harmonic resonance characteristics and the coupling relationship between each inverter in the condition of different parallel numbers of inverter. A method of notch control is proposed to suppress the harmonic resonance of the system. Simulated results show that this method is good-effected in filtering, and can suppress the harmonic resonance of PV grid-connected system in the type of LCL filter; at the same time, the background harmonic noise of the grid is also well suppressed.