Damp-proof and enhanced coating was fabricated on the porous Si₃N₄ substrate by sol-gel method, with CaO-SiO ₂-B₂O₃ as adhesive and sintering aids. The phase structure of the coating was characterized by X-ray diffraction (XRD). The morphology of the coating was characterized by scanning electron microscope (SEM). The density, water absorption and porosity of the porous Si₃N₄ were tested by Archimedes method. The bending strength of the coating was measured with SANS materials testing machine. The dielectric constant and dielectric loss were measured with the LCR tester model YY2813B. The results show that the water absorption of the porous Si₃N₄ is decreased by 90.99% to 96.97%, the bending strength of the porous Si₃N₄ is increased by 9% to 22%, the density, dielectric constant and dielectric loss of the porous Si₃N₄ are influenced little by sealing process.