Abstract: In order to solve the problem that recastation layer can not be eliminated in traditional process, ultrafoot picosecond laser was used to do the drilling experiment of Al₂O₃ ceramics in water medium. Compared with the drilling results in the air, the influences of main parameters such as single pulse energy and scanning frequency on pore size, taper and thickness of ceramic micro pores were analyzed. Interaction mechanism between picosecond laser and Al₂O₃ ceramics and material removal mechanism with different media were analyzed and discussed. The results show that, the diameter of laser drilling in water medium increases by about 35μm, micropore taper reduces to 1.04° and the effect of no reclamation layer drilling can be obtained. The presence of water in the process of laser drilling can cause vacuolization, absorption and transportation.It can effectively prevent the secondary adhesion of erosion material, eliminate re-cast layer and reduce micro-hole taper and improve the quality of micro-porous. The study describes the specific impact of water-assisted laser drilling and deepens the understanding of the mechanism of water-assisted effects.