Abstract: The rolling process characteristics of the 2-roll vertical rotary piercing mill is described.A simplified formula for engineering calculation of the said piercing mill is derived with the procedures，i.e.， calculating the arbitrary minute section of the contact surface between the piercer roll and the work piece，and then making the adding up；conducting the simple integral along with the rolling line and without consideration of the effects by the plug and circling zone so as to finally find out the deformation contact area.The calculation result from the said engineering formula is verified by means of comparison with the actually site-measured rolling data.The verification result shows that the formula is worth using as reference basis for design of the piercing mill.