The invention discloses a cylinder body machining fixing device, and belongs to the technical field of tool devices. The cylinder body machining fixing device comprises a supporting base. A limiting groove matched with the end of a flange on the outer side of a rotation workpiece is formed in the top of the supporting base. A rotation ring is arranged on the portion, located on the periphery of the limiting groove, on the supporting base in a rotating mode. A plurality of fixing shafts fixedly arranged on the supporting base are arranged between the rotation ring and the rotation workpiece. A pressing block is restrained and installed on each fixing shaft. Each pressing block comprises a force exerting end extending towards the rotation ring, and a pressing end extending to the flange on the outer side of the rotation workpiece. Wedge-shaped blocks corresponding to the pressing blocks one to one are arranged on the rotation ring. A power device used for driving the rotation ring to rotate is arranged on the supporting base. By means of the cylinder body machining fixing device, rapid alignment can be conducted, multiple pressing plates can be clamped at a time, the self-lock function is achieved, operation is simple, machining efficiency is improved, and the cylinder body machining fixing device is widely applied to machining of the rotation workpiece such as a cylinder body.