The invention provides an oxidation method for the purification process of a three-dimensional graphene coated single-particle nano-diamond material. The method is applied to a purification process consisting of magnetic separation, acidification, oxidation, alkalization and heavy liquid separation. In an oxidation process, an oxidizing solution with small oxidizability is employed for oxidation treatment, after oxidation, the oxidized mixed solution is filtered and cleaned by adopting filtration equipment and combining purified water so as to remove amorphous carbon from the mixture, thus providing favorable conditions for subsequent further purification. As the adopted oxidizing solution has small oxidizability, the oxidation method provided by the invention can reduce corrosion damage to oxidation equipment, prolong the service life and save the cost, also effectively removes amorphous carbon from the mixture, and improves the purification rate.