Abstract: In the heat-proof and wave-transparent materials for the antenna housing used under high Ma conditions, SiO₂ is added to the porous Si₃N₄ composite ceramic as the additive. The porosity, the pore size distribution, the phase composition, the microstructure, the mechanical properties, and the wave permeability of porous Si₃N₄ composite ceramic are studied by adjusting the content of SiO₂. It is shown that with the increase of the content of SiO₂, the porosity of the porous Si₃N₄ composites decreases, the bending strength increases, and the wave permeability first increases and then decreases. The introduction of SiO₂ not only promotes the sintering process but also improves the mechanical and dielectric properties of the porous Si₃N₄ composite ceramic. With Si₃N₄ being combined with 7.5 wt% SiO₂, better desirable mechanical and dielectric performance is achieved.