Porous silicon nitride ceramics were prepared by hot pressing process at low temperature using CaF2 as a sintering agent fora-Si₃N₄ powder．The effects of the content of sintering additives on the apparent porosity and bending strength of porous silicon nitride ceramics were studied，the composition of the materials and the fracture structure were analyzed． The results show that under the conditions of temperature 1450 ℃ and pressure 0.55T，when the addition of CaF2 is 6.0 wt%，the performance of porous Si 3 N 4 ceramics is excellent，the porosity of porous Si3N4 ceramics is 38．8%，the phase transition degree of a-Si₃N₄→β-Si₃N₄ is 38．5%，and the bending strength is 137.1 MPa．