Abstract: The microstructure of 3D needling felts is beneficial for the wave absorption. Wave absorbing composites with high temperature resistance could be formed by using carbon and boron nitride matrix with 3D needling carbon felts as reinforcement. In this paper, porous 3D needling carbon/carbon composites (C/C) were fabricated by precursor infiltration pyrolysis (PIP), then C/C--BN composites were fabricated by introducing BN into the porous C/C by using chemical vapor infiltration (CVI). The effects of CVI time on the microstructures, mechanical properties and dielectric properties of 3D needling C/C--BN were studied. With the increase of CVI time, the density and flexural strength of C/C--BN increase, while the porosity decreases. When CVI time reaches 160h, C/C--BN attains a density of 1.43g/cm³, a total porosity of 25%, and a flexural strength of 82MPa. Because of the decrease of porosity with the increase of CVI time, the dielectric constant of the C/C--BN composite increases and the dielectric loss decreases.