Abstract: X80 pipeline steel was girth welded with self-made self-shielded flux cored wire. The weld formation, microstructure and mechanical properties of the joint at different welding positions were analyzed. The results show that the weld at different welding positions had good formation, indicating that the wire had good all position welding adaptability. The microstructures of the weld at different welding positions were almost the same. The cap layer consisted of lath bainite and acicular ferrite; the fine granular bainite and quasi-polygonal ferrite were in the filling layer. The fine-grained heat-affected zone had almost the same microstructure of fine-grained ferrite and acicular ferrite. The coarse lath bainite and granular bainite were in the coarse-grained heat-affected zone, and the grain size of this area at vertical position was smaller than that at flat and overhead positions. The average hardnesses of weld and heat-affected zone were 226, 227 HV, respectively, which were slightly lower than that of the base metal (233 HV). The average impact absorbing energies at -10 ℃ of weld and heat-affected zone at vertical position were higher than that at flat position. The tensile strength of joints at different welding positions was similiar, and the tensile fracture of the joints showed ductile fracture characteristics.