The work aims to investigate the effect of chemical reaction rate on SiC chemical mechanical polishing (CMP) in the process of ultraviolet photocatalysis assisted polishing. The effect of ultraviolet catalysis on the material removal rate of (MRR) of polishing wafer was studied by three kinds of irradiation modes: no irradiation, polishing disc irradiation and polishing slurry irradiation. The Oxidation-reduction potential (ORP) value of photocatalytic reaction under different conditions was measured to characterize the photocatalytic reaction rate. The ultraviolet photocatalysis assisted polishing experiment of single crystal SiC wafer was carried out to investigate the effect of photocatalysis rate on polishing performance. From the experimental results, the material removal rate was increased by about 14%~20% with ultraviolet photocatalysis. With the increase of material removal rate, the effect of ultraviolet photocatalysis assistance on material removal rate became smaller. The material removal rate under polishing slurry irradiation was obviously higher than that under polishing disc irradiation. The polishing results under different conditions showed that as the the chemical reaction rate became faster, the ORP value of the solution became higher, the material removal rate became larger, and the surface roughness became lower. Under the conditions of polishing slurry irridation, H2O2 concentration of 4.5vol%, TiO2 concentration of 4 g/L, light intensity of 1500 mW/cm2 and pH11, the smooth surface with roughness of Ra 0.269 nm could be obtained after 120 min polishing with W0.2 diamond abrasive. In the process of ultraviolet photocatalysis assisted polishing of single crystal SiC, with the faster photocatalytic reaction rate, the solution ORP value is higher, the polishing efficiency is larger and the surface quality is better. Among the four factors such as H2O2 concentration, TiO2 concentration, light intensity and pH, H2O2 concentration has the greatest influence on the polishing effect, and the light intensity mainly affects the time for photocatalytic reaction to achieve stability.