Silicon carbide (SiC) is a promising candidate for large-scale mirrors due to its high stiffness and thermal stability. However, it is very challenging to obtain a super smooth surface for high precision optical telescopes due to the intrinsic defects of SiC. In this letter, a super smooth surface with a roughness lower than 1 nm and a surface profile of \lambda/50 is achieved by depositing a uniform and dense silicon surface modification cladding by plasma ion assisted deposition (PIAD) on a lightweight concave reaction bonded (RB) SiC mirror, followed by a polishing procedure. Characterization data from the high resolution optical microscope, WYKO profilometer, Zygo interferometer, and nanoindentation are further discussed. The thermal shock resistance test indicates that the surface modification cladding is very stable and shows firm adherence. A reflectance of over 98% in the visible light region is obtained on the spectrometer after being coated with the silver-enhanced coatings.