Abstract: Based on relevant actual circumstances of the piercing mill located a certain domestic company, and starting with the space geometry of the roll and the guide shoe, the mathematic method for designing the guide shoe is mainly described.The basic parameters such as the deformation zone length, the inlet obliquity and the oblique angle, and the width of the guide shoe are calculated.As a result, it is identified that the basic dimensions as determined with the mathematic formula are more scientific than those as obtained with the empiric method.Such basic dimensions ensures a better closure of the guide shoe groove, which can prevent chain band or tail end breaking in case of production of light-wall pipes.