Abstract: The welding stress and distortion,which appeared during the butt welding of girth joint of aluminum alloy cylinder under and without pre-tension stress,are numerically simulated by using ANSYS finite element analysis software.The calculation results show that pre-tension welding can reduce the welding residual stresses and deformations effectively.When the pre-tension stress =90%R_p0.2,the residual stress at weld is about 52% lower than that without pre-tension.Meanwhile,the welding deformations of aluminum alloy barrel are reduced greatly under pre-tension.