A combined fixture for preliminary machining of an impact specimen belongs to the technical field of a lathe machining fixture and is used for the lathe machining of the impact specimen. The technical scheme of the utility model is that the combined fixture consists of a fixture and a specimen clamping block, wherein the upper part of the fixture is a jaw, the lower part of the fixture is a clamping handle, the jaw is a flat metal plate with a certain thickness, the surface of the flat plate is vertical to the axial direction of the clamping handle, a rectangular clamping groove is arranged on the upper surface of the flat plate, a jackscrew hole is arranged at one end of the long side of the clamping groove, the outer end of the jackscrew hole is arranged on the side surface of the jaw flat plate, and the specimen clamping block is a rectangular metal block with the length being matched with the width of the clamping groove. The combined fixture has the advantages that the specimen machining efficiency is improved by 3 to 4 times; the specimen machining precision can be ensured easily, is doubled and can better meet various standard requirements on the impact specimen; the combined fixture is easy to manufacture, has low cost, is convenient to use and has long service life; and the labor intensity for specimen machining is greatly lowered, the working efficiency is greatly improved, and the normal ordered production is ensured.