The invention discloses a friction stir welding device and a profile welding method. The friction stir welding device comprises a welding machine and a welding auxiliary mechanism. The welding machinecomprises a welding machine main shaft, an upper shaft shoulder, a stirring needle and a lower shaft shoulder, wherein the welding machine main shaft, the upper shaft shoulder, the stirring needle and the lower shaft shoulder are coaxially arranged from top to bottom. The welding auxiliary mechanism comprises a connecting arm and correcting mechanisms, wherein the connecting arm is arranged on awelding machine framework or is integrated on the upper shaft shoulder, and the correcting mechanisms are arranged on the connecting arm. The correcting mechanism located in front of the stirring needle or the correcting mechanisms located in front of the stirring needle and behind the stirring needle enable an ideal butt joint state for the stirring needle. The friction stir welding device and the profile welding method ensure the convenience of welding like zipper-type sewing.