The invention relates to the field of ship manufacturing tools, in particular to a ship board jointing seam welding run-off tab clamping device. The ship board jointing seam welding run-off tab clamping device comprises a bottom board used for supporting a run-off tab and determining the mounting position, and a top board fixed to the bottom board; and the top board positions and fixes the run-offtab from the horizontal position and the front-and-back position and connects and fixes the clamping device and a welded part. The run-off tab is installed and fixed through the bottom board and thetop board, the clamping device is fixed to the end portion of the welded part, the seam welding run-off tab is placed well and fixed with a fastening device, then subsequent welding work can be conducted, the traditional mode for fixing the run-off tab and the welded part in a welding mode is avoided, no welding feature is left only by cutting a submerged-arc weld joint after welding is finished,the grinding workloads are reduced, the work efficiency is improved, and the clamping device can be reused and advantageously saves cost.