Abstract: Although it is rather difficult to shape the strip steel with the prismatic formation process in case the width to height ratio of the rectangular pipe is ≥2,the roll can be re-used after repair,and thus prolong its service span to reduce tool consumption,i.e.enhancement of the operation cast-effectiveness owing to this very formation process.Based on the 90 mm × 30 mm × 2.2 mm rectangular welded pipe,the basic design method for prismatic formation is discussed in case the width to height ratio of the rectangular pipe is ≥2.Relevant operation practice shows that employment of the said prismatic formation process is capable of producing high quality rectangular welded pipes,and that for roll with rather big linear velocity difference,its structure should be improved to suit different strip steel sizes.