Abstract: With Mg(NO3)2·6H2O, anhydrous ethanol and collodion emulsion used as starting materials, solvent and surfactant, respectively, the MgO sol was prepared by sol-gel method. Then the MgO sol was coated on the surface of the ceramic skeleton of 3D-SiC by dip-coating process to get MgO nanofilm after roasting. The phase composition and microstructure of the nanofilm were investigated via XRD and SEM. The results showed that the smooth and compact MgO nanofilm whose thickness ranges from 0.8 to 1.0 μm can be deposited on the surface of 3D-SiC as substrate the way the substrate should be eroded in HF solution for 30 min to make sure that the coated MgO sol has the mass ratio of Mg(NO3)2·6H2O to collodion emulsion is equal to 1.0, then it is dried at 80°C for 10 min and, later on, at 480°C for 10min and roasted at 800°C for 1 hr. The MgO nanofilm is bonded well to the substrate, and its average particle size is about 500 nm.