Abstract: Described are the main aspects of the Ф600 mm piercing mill line,including the main technical parameters and the characteristics of its structure as a whole. Also detailed and analyzed are the structure design concerning the key techniques as employed by the mill line,which involve the new type bar/plug pre-rotating device and the process,the upper and lower guide shoes,the housing and rolls of the mill proper. It is proved through the site operations that the piercing mill is capable of consistent running with all the target values up to the design requirements,and having high economic profitability,particularly in case of producing seamless steel pipes with OD above 400 mm.