Abstract: In order to improve oxidation-resistance of diamond grit,interface reaction process, composition and structure between Ti,Mo and W coating and diamonds are studied by XRD,SEM,DAT and TGA.Influence of Ti,Mo and W coating on oxidation of diamonds is investigated.Test results show that reactions between Ti,Mo and W coating and diamonds occur separately above 600,650 and 650℃.Corresponding epitaxial TiC,Mo₂C+MoC and W₂C+WC films grow on diamonds surface reaction diffusion process.These high oxidation resistant carbides films prevent diamonds from oxidation.The diamonds with Ti, Mo and W coating oxidate in air separately above 958,871 and 880℃.After these diamonds with coatings are treated in vacuum with carbon,oxidation temperature of diamonds with Ti,Mo and W coatings are separately 1024,977 and 986℃.