Abstract: Based on the geometric model established for rotary roiling of high helical finned tubes, the motional behavior of a rolling piece in the deformation zone was investigated, and the results show that the phenomena of axial elongation has a connection with the distribution of circumferential velocity. It is the essential reason to make a rolling tube elongate along the axial direction that the axial velocity in the deformation zone increases along with the circumferential velocity in the condition that the pitch value of the groove keeps changeless along the axis. A formula of axial elongation rate was given on the basis of theoretical analysis. In order to verify the formula of elongation rate, rolling experiments for two types of rolling pieces in different reductions were conducted and the results approximately agreed with the theoretical values.