The invention discloses a fixing device for machining a locating hole of a gear. The fixing device comprises a workbench, a lead screw, bearing pedestals, a handle, sliding blocks, connecting rods and press plates. A strip-shaped groove is formed in the middle of the workbench. The lead screw is mounted under the strip-shaped groove of the workbench through the bearing pedestals. The handle is mounted at one end of the lead screw. The two sliding blocks are mounted on the lead screw and each vertically welded to the corresponding connecting rod. The connecting rods penetrate the strip-shaped groove of the workbench. The upper ends of the two connecting rods are fixedly connected with the press plates. A thread on the lead screw is divided into two parts with the lead screw as the middle point, and the two thread parts are opposite in direction. A triangular gap is formed in one side of each press plate, and the triangular gaps of the two press plates are opposite. The fixing device has the beneficial effects of being simple in structure, reasonable in design, capable of being used for gears of different specifications and easy to utilize and popularize.