Abstract: CVD diamond has been widely applied in various fields.Despite several existing processing methods,many problems,such as low efficiency and poor precision,still arise in actual applications.To avoid the problems of the existing methods for polishing diamond,this study prepares a new type of slurry for polishing diamond using TiO₂ photocatalytic oxidation theory.Firstly,the apparatus is set up according to the mechanism of photocatalytic oxidation.Then,the slurry is characterized with the methyl orange solution and the oxidation-reduction potential(ORP)analyzer.Finally,the CVD diamond is polished with the photocatalytic assisted chemical mechanical polishing method.The results show that P25 TiO₂ photocatalytic shows the best oxidation activity.The effect on catalyst activity is obvious when adding 1 mL of H₂O₂ and 0.2 mL of H₃PO₄ per 100 mL water,and the oxidation ability is the best.The CVD diamond is polished smoothly by using the new slurry.