Abstract: Addressing the commonly-used several geometrical models for the rotary-rolling pipe elongating mill, four mathematic equation sets are used to conduct the calculation of the longitudinal and transversal velocities at the roll-material contacting points in the deformation zone, and quantitatively analyze the shortcomings of each model. Based on the analysis, the four equation set are again employed to make the calculation for optimization purpose, resulting in a new reasonable geometrical model for the rotary-rolling pipe elongator, and thus providing a new approach to improving thereof.