To realize the super-smooth polishing of chemical vapor deposition silicon carbide (CVD SiC), nano-scratch test is applied to study the critical load for brittle-ductile transition, and its polishing mechanism is analyzed according to the force on an abrasive grain. Furthermore, the influencing factors on the surface roughness are systemically investigated by experiments from the aspects of material characteristics, processing parameters and pH values of the polishing fluids. The research results show that the polishing mechanism for CVD SiC in a steady polishing process is a ductile scratch process of abrasive particles on the surface of CVD SiC. The inhomogeneity of CVD SiC grains and surface high spots degrade the surface finish. The surface roughness increases near-linearly with the abrasive particle size in a certain extent, and increases with the hardness of polishing pad. However, the effect of polishing pressure on surface roughness is related to the deformation behavior of polishing pad, i.e., when polishing pad has an elastic or elastic-plastic deformation, surface roughness increases with polishing pressure in a narrow range; when polishing pad has a plastic deformation, polishing pressure has no obvious effect on surface roughness. In addition, polishing velocity and the pH value of polishing fluid have little effect on surface roughness. The research results provide a quantitative experimental basis for the optimization of selecting processing parameters during the super-smooth polishing of CVD SiC.