Silicon carbide has good physical, mechanical and thermal properties, it has been widely used in aerospace field in recent years. In order to meet the requirements of optical performance of space remote sensor, silicon carbide surface is usually treated by surface modification technology for further implement requirements, this process is called modification. There are two ways of modification: PVD and CVD, the purpose is to cover the surface voids of silicon carbide with a modified layer, reducing surface roughness and suppression of surface scattering, improving imaging quality of optical system, improvement of resolution, reducing the loss of light energy .Now, modification technology is mature, but there are still risks in the modification process, there are also corresponding processing risks in the optical polishing process after modification. In order to investigate the influence to pitted reaction bonded SiC (RB-SiC) without SiC or Si cladding layer, 10nmCr, 10nmTi, 10nmGe and100nm Ag films are deposited using thermal evaporation method. The research results show that Ge can decrease the roughness of RB-SiC surface and has preferable smoothing effect of silver thin film comparing to that of Cr and Ti. This article through the research, a method of direct application of non-modified silicon carbide substrates in production practice is explored. The essence is to utilize the growth characteristics of materials, complete growth in the hole, achieve the purpose of filling holes, then the surface roughness is reduced and the surface scattering is suppressed.