The utility model belongs to the forging field, and particularly relates to a forming device for a straight-edged tapered cylinder forging of a nuclear power evaporator, which is suitable for process design and production course of forming of a straight-edged tapered cylinder forging of a nuclear power evaporator or a hydrogenation reactor. The device comprises a trestle, a saddle and a twist correction block. The device adopts the structure that the saddle for inserting into a hole in the center of a forging blank is placed on the trestle which is matched with an upper flat anvil arranged on the outer side of the forging blank for use; the twist correction block placed on the base of the trestle is matched with the saddle for use, the twist correction block is located in the position to ensure that the axis of the forging blank and that of the saddle are always in the same plane and maintain a certain angle which is in accordance with the taper of the final part. The device has a simple structure, and solves the problem of difficult forming of the straight-edged tapered cylinder forging; and by adopting the device, the forged straight-edged tapered cylinder forging has uniform admittance and all the sizes meet the requirements of the parts.