Abstract: Discussed are several control methods as used for improving outer dimensional accuracy, welding quality and surface quality of the ordinary and sharp-angled cold-bend rectangular steel tubes, involving such aspects as raw material, rolling groove, operational tools, welding process parameters, and inspections for weld seam quality, etc.Actual operation practice shows that consistent and accurate formation which ensures better outer dimensional accuracy of the tube are obtained by means of adapting the oblique-inserted roll, using the box-shaped roll for finishing-formation, summarizing the optimum formation parameters, and optimizing and modifying structures of the mounting-frame of the side vertical roll, the vertical roll base and the rolling mill frame;the welding quality of the pipe is stabilized by means of improving steel strip quality and optimizing the welding process;and surface quality of the cold-bend rectangular tube is improved by means of properly selecting rolling dies, guaranteeing cleanly utilizing circulation cooling water, and optimizing the conveyance roller table, etc.