Abstract: Elaborated here in the article is the construction status of a domestic Φ100 mm 3-roll mandrel pipe mill line, involving such aspects as the product mix, the technological schedule and the characteristics of the major equipment units as selected. It is regarded via relevant analysis that the said mill line is capable of producing steel tubes with high geometric dimensional tolerances,and producing finished tubes with minimum wall thickness up to 3.5 mm.After two month continuous operation,the production cycle of the mill line has been up to 35 s/piece,being very close to the expected target. The steel tube cropping loss rate is within 3%~5%,while the actual yield is 90.0%~90.5%,which indicates that the amount of the straggling steel tubes has to be well controlled so as to further enhance the yield.Finally it is pointed out that the existing tunnel-shaped frame of the mill causes rather difficult and time-killing roll-stand change operation of the mill,and accordingly the roll-changeover device has to be optimized to reduce the said difficulty and the roll changing time.