Abstract: Based on the deformation characteristics of the steel tube in the process of slight stretch sizing (reducing), the MSC.Marc software is used to conduct the FE analysis of the 3-D elastoplasticity for the purpose of simulating the deformation process of steel tube going through the 14 stand slight stretch sizing (reducing) mill. The internal polygon severity is investigated via the study of the transverse wall variation on the tube cross section. And on the basis of analysis of the axial wall variation over the full length of a single tube, the crop lengths of the thickened front and tail ends can be directly measured with the FE model instead of analytical calculation. As a result, product defect analysis and process design instruction will be available.