Abstract: Addressing the Ф720mm rotary expanding pipe mill, relevant math model is set up, and the simulation analysis is conducted with the 3-D finite element simulation technology, by which the steel pipe deformation data are obtained. Based on the result of the said research activities, the main deformation and the additional deformation of the pipe rotary expanding process are calculated, and accordingly, the rationalities for determination of the values of toe angle β and the adjustable distance of vertical movement of the rolls h as well as the corresponding tool design are discussed from the perspective of deformation. The analysis results will be helpful to further identifying the technological nature of the pipe rotary expanding process so as to further improve the product quality.