Abstract: With the space analytic geometry data and the vector theory,the equation of the roll contour line is derived.Also studied is the sufficient condition which ensures that in the deformation zone,the workpiece is running forward straightly with neither twisting nor rotation movement,i.e.,proper roll profile together with adequate speed ratio.In addition,the original structure of the planetary mill is modified with introduction of the concept of supporting sleeve so as to improve the dimensional accuracy of the workpiece.This design idea is simple and easy to be implemented,being an effective way to design the 4-roll planetary pipe mill.