In order to obtain good appearance and anti rust performance, a layer of reaction film can be formed on the surface of motorcycle sprocket by using the waste heat of workpiece during quenching or tempering. By using the new quenching oil, a kind of reaction film can be formed on the surface of gear during the quenching process, so as to improve the anti friction performance and surface state of the gear. The quenching oil is ordinary vg220 quenching oil and a new type of graded quenching oil. Phosphate compound additive is added to the ordinary vg220 basic quenching oil to form a protective film on the surface of the workpiece. When the quenching temperature is 120c, phosphate compound can be added to the quenching oil to form a compound on the surface of the treated workpiece. Therefore, the compound formed by quenching in this oil can improve the anti-oxidation and adhesion resistance, friction and wear resistance and fatigue pitting resistance of motorcycle sprocket. It is suitable for those products which need not be ground after quenching and tempering.