Abstract: In order to ensure that the straightness of the UOE large-sized welded pipe is≤0.05%L,a straightening machine for the large-sized welded pipe is designed,developed and manufactured.Elaborated here in the article are the main aspects of the straightening machine,including the structure,configurations of the mechanical and hydraulic equipment,the electrical structure and the control system,the equipment features,and effectiveness of actual operation.The theoretical straightening force and the actual one of the tubes with representative sizes are comparatively analyzed.It is regarded via the analysis that thanks to the said straightener,all the problems as encountered with during the straightening process of the tube are solved,including scratch and indentation,over-tolerance ovality of the pressed section,impact from hydraulic unloading,and the abnormal vibration of the gantry,etc.The straightness of the tube as straightened is≤0.05%L,being up to the applicable requirements for manufacture of the high value-added steel tubes.