Abstract: According to the deformation characteristics of the seamless steel tube during the stretch-reducing process, a three-dimensional thermo-mechanical coupled finite element analysis model is built up with the MSC.Marc software for numerical simulation of the trial pipe-rolling process of the 25-stand stretch-reducing mill.The results of simulations with different stand spaces indicate that the micro analysis model as set up with the said software is accurate, and its reliability is further verified via relevant testing.And thanks to studying the changes of tube end tension and the working diameter of the roll, the thickening mechanism of the tube end is identified.Furthermore the influence by various factors on the tension is discussed, and the law of tension formation analyzed.The research results provide a basis for future developing the technology for control of tube end wall thickness.