The gear sleeve of automotive synchronizer is difficult to process. In this paper, the processing technologies of gear sleeve in the world were introduced as well as the machining principle. The gear sleeve flying cutter cutting mathematical model was established. By means of strength and stiffness analysis, the stiffness is the most important checking target. Special constant stiffness cutting tool of the gear sleeve was designed for numerical control machine, and it is proved that the cutting tool is suitable for cutting.