Abstract: The derivation of the traditional modulation strategy for unipolar and bipolar single-phase inverters is based on the assumption that the DC bus voltage is an ideal constant DC parameter. However, due to the DC/AC power coupling, the DC bus voltage of the single-phase inverter contains a large amount of ripple component of double AC voltage frequency in the practical single-phase inverter. With the traditional modulation strategy, the second-order ripple component causes the increase of the thirdorder harmonic on the AC side, and impacts the power quality of AC output voltage. By means of the double Fourier transform method, the harmonic characteristics of output voltage are theoretically evaluated. Then, this paper proposes a harmonic reduction modulation strategy of single-phase inverter with a high second-order ripple rate of voltage on the DC side. Based on the third-order generalized integrator, the second-order ripple component in the DC bus voltage is extracted by the enhanced phase-locked loop（PLL）. By injecting the opposite second-order components into the modulation coefficient, the third harmonic and the total harmonic distortion（THD） of the output voltage have been reduced. Finally, the rationality and feasibility of the active modulation strategy are verified by experiments.