Abstract: The automatic welding test of girth weld of X80 pipeline was carried out by using self-developed ER80S welding wire. The quality, macro-and micro-structure and mechanical properties of the girth weld were studied. The results show that the girth weld has good appearance and good fusion between the weld and the base material, and between the weld passes. The root weld is composed of acicular ferrite（AF）+ granular bainite（GB）+ side lath ferrite（FSP）, the filler bead is composed of AF+GB, and the cover weld is composed of AF +GB +a small amount of FSP. The transverse tensile test and all-weld metal tensile test results show that high strength matching of girth welds can be achieved between the self-developed ER80S welding wire and X80 pipeline. The girth weld has good impact energy stability, the lowest impact energy of weld center is 127.5 J, and the impact fracture is ductile fracture. The crack Ti_p opening displacement of weld center and heat affected zone at different positions of the girth weld is bigger than 0.254 mm, and the girth weld has good fracture toughness.