Abstract: Under the assumptions of potential flow theory and of linear wave theory, the diffraction effect of porous plates array under the action of regular waves is investigated by applying the eigenfunction expansion method and Bessel function addition theory. Each plate in the array is rigid, porous, and fixed below the still water surface with negligible thickness relative to the incident wave wavelength. The fluid motion through its surface satisfies Darcy's law. Based on the derived velocity potential, further analytical expressions for the heave force of the plate and the free surface elevation of the flow field are obtained. The analytical solution is verified by the published calculation results of the isolated plate, after which the diffraction phenomena of the four-plates system are analyzed for various wave and structural parameters. It is shown that when the plate opening ratio, draft depth, and incident wave wavelength are within a certain range, significant interaction phenomena will occur inside the array, mainly manifesting as the shielding effect of the plate on the upstream side to the plate on the downstream side. At a specific incident wave number, the maximum reduction of the downstream plate droop force to 76% of the upstream plate can be achieved by selecting the appropriate spacing for the four-plates system. It is also found that the wave energy focusing phenomenon may occur on the upstream side plate in the four-plates system, causing a sharp increase in the free surface elevation, but this wave energy focusing phenomenon will gradually diminish with the increase of the plate opening rate.