Abstract: Objective The aim was to study high-efficiency automatic welding process of L415M pipeline. Methods Automatic root welding of D508 mm×7.1 mm L415M pipeline was conducted by argon tungsten arc welding, filling and covering welding of gas protected solid wire automatic welding process. Microstructure and mechanical properties of weld were tested after welding. Results The results showed that weld was well formed, microstructure of root weld was mainly acicular ferrite (AF) + granular bainite (GB), and microstructure of filling and covering weld was acicular ferrite + proeutectiod ferrite (PF) + granular bainite. Transverse tensile test all broke in the base metal and the maximum tensile strength was 576 MPa. Bending plastic deformation ability of welded joints was good. Weld and fusion line had good low temperature toughness. Hardness of weld center was higher than that of its adjacent heat affected zone and base metal. Softening phenomenon of heat affected zone existed in the covering pass. Conclusion High efficiency automatic welding of L415M D508 mm×7.1 mm pipeline could be realized by automatic root welding of argon tungsten arc welding + gas protected solid wire automatic filling and covering welding process designed in this study.