In order to avoid the influence of jack accessory welding on the size and roundness of inner hole of the cylinder after finish machining,the welding production technology suitable for the finished cylinder accessories was studied from the point of view of increasing rigid restraints,reserving reverse deformation and controlling welding heat input. The research shows that the product quality cannot be guaranteed only by using the small specification MAG welding process of I =140 ～160 A,U=20～22 V and v=210～230 mm/min,and the maximum welding deformation of 0.3 mm will still appear in the inner hole of cylinder. The welding deformation can be effectively controlled by using small specification welding and prefabricating 0.8 ～1.2 mm transverse reverse deformation with restricted tooling,so as to ensure that the size and roundness of inner hole of the cylinder meet the design requirements.