Abstract: The mandrel pipe mill is one of the important technologies in a seamless pipe manufacture. The technology of a semi-floating mandrel pipe mill represents advanced technique of seamless pipe manufactures, and it is a hot spot of research at present. The finite element simulations are made on technology of 6-stand semi-floating mandrel pipe mills of 109mm×7mm by ANSYS/LS-DYNA at 3D thermosetting coupling. Based on the analysis, the conclusions are reached that the max von Mises stresses on the pipe transverse plane occur at 4th and 5th stands; the max effective strains on the pipe transverse plane occur at the first three stands; the rolling forces at 3rd-5th stands are larger than other stands’; the rebound is occurred at pipe outside in the process of the diametric decrease; the temperatures distribute asymmetrically on one pipe transverse plane. This study provides a technical foundation to the improvement of technologies of mandrel pipe mills.