Abstract: The piercing & rolling combined process is such a one that piercing, rolling and reeling of pipes can be completed through a single pass in three roll cross mill. The piercing & rolling combined mill features a large amount of deformation and is suitable for producing high precise seamless pipes with small diameter, especially for producing hot rolled finished pipes with thick wall and strict requirements of dimesion and geometry. The main characteristics, three kinds of passes, testing pieces and piercing conditions of the mill are described. Tail triangle, flaring, inside and outside spiral marks as well as surface quality and dimensional accuracy during rolling are analyzed roughly.