Silicon nitride short fibers porous materials were fabricated by using boron nitride as sintering assistant with extraction and filtration method.The optimum sintering system was determined by analyzing the oxidation process of boron nitride and silicon nitride fibers.The microstructure, dielectric properties and compressive properties of different boron nitride content materials were investigated and analyzed. The results show that the oxidation weight of boron nitride increases 20%,the oxidation is obvious on the surface of silicon nitride fiber at 1 200 ℃.Silicon nitride short fibers are adhesived markedly along with increasing of the content of the boron nitride,the test result show the main components of bonding points are silicon dioxide and borosilicate.And with the increase of the density, the dielectric constant of silicon nitride short fibers porous materials increases from 1.36 to 1.62,tanδ increases from 7.8×10^-4 to 9.5×10^-4,the compressive strength of materials under 10% compressive strain improves from 0.58 MPa to 2.03 MPa.