SiC coating for surface modification grows on reaction boned SiC (RB-SiC) substrate cannot have high quality because the material of RB-SiC has two phases. We apply a new method to improve the effect of surface modification. First the surface of RB-SiC is carbonized, and then a diamond like carbon (DLC) coating is prepared on it before the growth of SiC coating. Research and tests show that the SiC coating can grow denser and uniform because of the buffer function of the DLC coating, thus the effect of surface modification is improved. The roughness reduces from 1.397 to 0.478 nm (rms) after the surface modification using DLC buffer layer.