Abstract: The girth welds of X70 pipeline were prepared by ER70S-G STT for root pass and E551T8-K2 self-shielded flux-cored wire for hot,fill and cap pass. The mechanical properties of girth welded joint were tested and counted,and the main influence factors of mechanical properties were analyzed. The results showed that the girth welded joint of X70 pipeline had better mechanical properties. The main factors that affected the mechanical properties were the weld defects such as slag inclusion,porosity and incomplete fusion. It was pointed out that the welding defects were not only related to the technological characteristics of self-shielded flux-cored welding,but also closely related to the welding operation level and quality consciousness.