Gas pressure sintering is applied to prepare arbitrary porous silicon nitride (Si(3)N(4)) ceramics using yttria (Y(2)O(3)) as the sintering additive and naphthalene powder as the pore-forming agent. The results obtained show that the porosity of the sintered porous Si(3)N(4) ceramics is 40%-54% when the Y(2)O(3) content is from 3 to 15 wt% and the sintering temperature is from 1700 degrees to 1850 degrees C. The bending strength is in the range of 60-226 MPa. The porosity of the porous Si(3)N(4) ceramics with Y(2)O(3) content of 9 wt%, sintered at 1800 degrees C, is increased to 51%-66% when the naphthalene powder content is 5-30 wt%. Finally, large and arbitrary porous Si(3)N(4) ceramics with a porosity of similar to 60% can be successfully fabricated by this method.