Abstract: Underwater hyperbaric welding was conducted, with the ambient pressure, welding current, composition of welding gas and electrode extension as variables, to investigate the influence on the weld bead geometry. The variation trends of weld penetration, weld width and reinforcement with the above variables were determined by orthogonal experiments. The results show that with the increase of ambient pressure, the welding spatters, weld penetration and reinforcement increased, but the weld width decreased. In hyperbaric environment, with the increase of welding current, the weld width did not change significantly, but the weld penetration increased and the reinforcement also increased slightly. With the increase of CO₂ ratio in shielding gas, the weld penetration decreased, the weld width increased, but the reinforcement had no obvious change. With the increase of electrode extension, the weld penetration decreased, the weld width and reinforcement increased.