Abstract: Briefed here in the paper is the general status of the Φ460 mm PQF mandrel pipe mill.Also described in detail is the development process of the 345 mm pass of the mill.It is regarded via the analysis that compared with the original 322 mm pass series, the newly designed and developed 345 mm pass series has made the expansion ratio of the piercer increased from 5.1% up to 11.43%, being more proper relatively;moreover thanks to the 345 mm pass, the piercer is capable of producing the shell with the minimal wall thickness of 22 mm;when rolling, it is suggested to increase the elongation of the piercing mill, and meanwhile decrease the elongation of the rolling mill proper so as to retard the tendency of occurrence of the defects like rolled pit and tearing during rolling the steel pipe with D/S over 40.