Abstract: The fork part is an important part of the lathe speed change mechanism; its main function is to match the gears on the two shafts with different speeds through the fork so as to achieve the purpose of speed change. In this paper, the structure of fork part is briefly analyzed, the embryo size and machining allowance are determined according to the technical requirements of fork, then the optimal processing scheme is determined through comparative analysis, and the processing process route of the scheme is formulated. The special fixture of milling machine is designed for the processing of fork slot. The fixture has simple structure and can be quickly clamped; it can improve the production efficiency under the premise of ensuring product quality.