The harmonic problem caused by the multi-inverters grid-connected to the power grid in point of common coupling is studied. Small-signal circuit model for single inverter and multi-inverters is established. The equivalent impedance of transfer function of the inverter, PWM switching harmonic source and power grid are derived. The equivalent output impedance of amplitude-frequency characteristic and phase frequency characteristics of the inverter and PWM switching harmonic source are analyzed by Bode diagram. The harmonic of 35 kV photovoltaic power station multi-inverters grid-connected system under the different conditions is analyzed in Matlab/Simulink. The simulation results show that if the grid-connected inverters are more, the current harmonic distortion rate of PCC will be greater. It mainly contains low-order harmonic but less high harmonic. The effectiveness of small-signal circuit model is verified.