In this study, we propose a water-assisted laser micropore processing method to address the problems of severe deformation of the metal filter screen, the large tapering and poor shape consistency of the micropores when lasers are used to process massive micropores on the metal plate. The micropore processing quality can be improved based on the capillary phenomenon of the water entering the micropores, the reflection and refraction phenomena of light at the gas-liquid interface, the force and cavitation effects generated by the irradiation of laser into the water, and the cooling effect of the water. Herein, perforation experiments were conducted on a 304 stainless steel plate with different thicknesses using a picosecond pulsed laser with and without water assistance; thus, the feasibility of water-assisted laser processing can be confirmed. The experimental results denote that the micropore tapering obtained by the water-assisted method is reduced by approximately 2°--6° and that the recast layer and the heat-affected zone reduce compared with those obtained by direct laser drilling using the same processing parameters. Further, the amount of deformation of the processed filter screen is reduced, and the consistency of the micropores is improved. Finally, a filter screen containing a large number of micropores having an exit pore size of 55 μm is realized on a 60-μm-thick sheet using the process parameters optimized via an orthogonal experiment.