This standard specifies a method for the determination of the amount of cerium oxidation in rare earth polishing powders mainly based on cerium-based rare earths, which is suitable for polishing powders with cerium oxidation content ranging from 40% to 99%. The principle of the method is to dissolve the sample with phosphoric acid and oxidize trivalent cerium to tetravalent cerium by perchloric acid. In 1 mol/L sulfuric acid medium, benzene-substituted anthranilic acid is used as an indicator, and the ferrous sulfate ammonium standard solution is used for titration to the end point to determine the content of cerium oxidation. The required reagents and their preparations are listed in detail in the standard, including phosphoric acid, perchloric acid, sulfuric acid and ferrous sulfate ammonium.