Abstract: The occurrence of the groove wear on the flank face of diamond cutting tool makes a serious impact on the quality of the finish surface of the workpiece. In order to reveal the growth and extension mechanism of the groove wear from the perspective of graphitization, the molecular dynamics (MD) model of diamond cutting tool with initial groove on the flank face is established, and the motion of the workpiece material and the change of crystal structure of the diamond cutting tool are simulated. The results show that the motion of the workpiece material changes for the existence of the initial groove, and the temperature and the energy of the atoms increase in the cutting process, nearly 8% for the temperature and 1.4% for the energy. The analyses of crystal structure and the radial distribution function of the diamond cutting tool show that there is a diamond-graphite transformation on the initial groove. The change of the graphitization conversion with cutting time is studied through bond angle calculation. The graphitization conversion rate increases with cutting time, when the cutting process proceeds to the stable stage, the graphitization conversion rate tends to be stable at nearly 6%.