Abstract: Addressing the main problems of the full-floating mandrel mill operation line located at the facility of Baosteel tube plant,i.e.,“bulging” and poor wall thickness uniformity of the tube,effective measures have been taken to eliminate the said defects,including improvement of mandrel lubrication conditions,self-developed non-conventional grooves of the stretch reducing mill,development of large-sized grooves and expansion of hi-chromium steel product lines,improvement of the automatic process control level of the mill line as well as continual technological modification,etc. As a result the capacity of the said mandrel mill line has been well tapped to produce hi-precision and hi-grade steel tubular products for the customers.