The invention discloses an arc-shaped wall plate vertical assembling butt-joint longitudinal weld seam welding device, and relates to the fields of aerospace product machining process equipment and positioning. The welding device comprises a servo motor, a transverse adjusting lead screw, a rotary platform, a fastening tool, a head end fastening mechanism, a lifting motor, a stand column, a tail section fastening mechanism, a lathe bed and a lathe bed adjustor. The lathe bed adjustor is fixedly mounted at the bottom of the lathe bed. The transverse adjusting lead screw is fixedly mounted on the upper surface of the lathe bed; the output end of the servo motor is fixedly connected with one end of the transverse adjusting lead screw. The rotary platform is fixedly mounted at the upper end ofthe transverse adjusting lead screw. A to-be-welded workpiece is fixedly mounted on the upper surface of the rotary platform. The fastening tool is fixedly mounted at the axis of the welded workpiecein the axial direction. The lifting motor is fixedly mounted in the front section of the stand column. By design the structure form of connecting joints between tank body barrel section arc-shaped wall plates, the connecting joints are more suitable for the friction stir welding process, a special welding tool is designed, and the pre-welding assembling and welding quality are ensured.