Abstract: Analyzed here in the article are the causes for the“Hexagonal Bore”defect as encountered with during the production of the hot-rolled seamless steel pipe,and the solution for it.It is concluded as follows via the analysis.Since the start-up of the production line,as limited by the roll stand allocation and the product range requirement,etc.,it has been not so easy to fix the said“Hexagonal Bore”defect problem just by correcting the general reduction amount or the individual stand reduction amount,which is not the best optimization way.Given the specific reduction ratio and the general reduction ratio are designed,optimizing the pass ovality will get the said defect obviously alleviated.The bigger the ovality,the higher possibility for the defect to occur.