The invention discloses a harmonic suppression method for a grid-connected photovoltaic inverter. The harmonic suppression method comprises the steps of performing evaluation on power grid impedance to obtain a power grid impedance estimation value; detecting the voltage of a power grid, and separating out a grid side harmonic voltage component from the voltage of the power grid; obtaining a grid side harmonic current estimation value according to the ratio of the grid side harmonic voltage component to the power grid impedance estimation value; taking a superposition value of the grid side harmonic current estimation value and an inverter side harmonic current as a current control instruction value; performing repeated control on the difference value between the current control instruction value and the inverter side output current, and overlaying with the voltage of the power grid to obtain a modulation wave signal; and performing compensation on the harmonic current in the power grid through closed loop control according to the modulation signal. The harmonic suppression method provided by the embodiment, without requiring a current transformer and an active filter in the power grid system, has good harmonic compensation effect and low compensation cost.