Mechanism of catalytic action of transition metals on the diamond graphite is explained from the perspective of the electronic and atomic. That is, transition metals have empty d orbitals and some plane meets the aligned principle with the (111) plane of diamond structure. In order to verify the conclusion, models of chromium, iron, cobalt, titanium, platinum, aluminum, copper atoms and diamond structure are established based on the first principle. By simulation calculation, regularities of diamond graphitization with the action of different atoms are gained. The simulation results show that with the action of Cr, Fe, Co, Ti and Pt atoms, phenomenon of graphite appears in diamond structure in varying degrees. Al and Cu atoms have no effect on diamond graphite. Plane degree of the diamond structure with the action of metals ascends followed by iron, chromium, cobalt, titanium, platinum, aluminum, copper. The variance of the distance between interphase carbon atoms ascends followed by iron, chromium, cobalt, platinum, titanium, aluminum, copper. Changes of the system energy of the optimized system descend followed by iron, chromium, cobalt, platinum, titanium. By comparison, the iron, chromium and cobalt atoms have obvious catalytic effect on the diamond structure, and platinum and titanium atoms have some catalytic effect, and aluminum and copper atoms have no catalytic effect. When the metal has unpaired electrons in d orbitals and meets the aligned principle on a certain surface, with the increasing of the number of unpaired electrons, it has greater catalytic effect on the diamond structure. On the other hand, when the metal valence electron layer has no d orbital or the d orbital is full, it has no catalytic effect on the diamond structure. The research provides a theoretical basis to machine diamond tools with the use of diamond graphite mechanism.