Abstract: Experiments on polishing and surface-modification of an aspheric surface silicon carbide (SiC) mirror with 520 mm diameter and some SiC plane mirrors with different diameters were carried out, the technology of surface-modification was analyzed and discussed in detail. The effect of surface-modification (ion beam assisted deposition) on optical properties of SiC mirrors was researched. Several types of association scheme were constituted by combining the physical and chemical behavior of physical vapor deposition (PVD) coatings with the mirror polishing technique, the PVD coatings- requirements for the surface properties before surface-modification and the optimum combining site between them were mainly studied. Results show that the polish of modified surface with suitable plan can both improve the surface error and roughness. The surface roughness of 520 mm aspheric surface SiC mirror is 0.756 nm (Sq). Compared with the surface before modified, the roughness is improved.