Abstract: The paper gives a description with respect to the "over-plus wall thickness deviation" during pipe rolling process with mandrel, introduces the concepts of "over-plus wall thickness deviation" and "wall thickness deviation in the same mill stand", also carries out an analysis of the influence of "over-plus wall thickness deviation" on the wall thickness tolerance of the cold drawn tube and the metal yield, there by a mathemantic expression for calculation of the value of "over-plus wall thickness deviation" and the actual wall thickness of the tube is deduced.