Moving cloud shadows in the region where a large-scale PV power plant is located will cause the DC voltage output of some PV arrays to be perturbed, and the inter-harmonic component will be output to the grid, which will lead to sub-synchronous oscillations of PV power generation systems that are normally operated at the same grid. In this paper, firstly, the output characteristics of PV arrays under moving cloud shadows are investigated, and the generation mechanism of inter-harmonics in PV power generation system is analyzed through the small-signal perturbation model, which elucidates the reasons for the occurrence of sub-synchronous oscillations in PV power generation system triggered by the inter-harmonics; secondly, the influence of the change of the sub-synchronous oscillation frequency on the resonance suppression strategy is explored, and a sub-synchronous oscillation suppression strategy based on the proportional resonance control is designed for suppression of Finally, the effectiveness of the proposed suppression strategy is verified by simulation.