Abstract: GMAW(gas metal arc welding) progress was fluently executed under the range of 0.1-0.7 MPa air pressure shielded by CO₂ and 80% Ar+ 20% CO₂ gases,which were tested by the igniting and exploding experiments using a hyperbaric cabin to simulate the underwater conditions.The arc characteristics of the GMAW were studied in hyperbaric conditions to discover the law of the arc affected by the environment pressure,the welding current,the stick-out,the gas type and the gas-flow.The experiments results were also given,and a mathematical model under the high-pressure air condition was found by using the least square approximation method based on the experimental data.