Abstract: This paper studied gas tungsten arc welding under 1 -700 kPa air pressures.Explosion test indicated that hyperbaric air is not explosive but the flammability of objects within the chamber is greatly increased, so some explosion-proof measures have been taken in the hyperbaric welding test chamber.With much stronger Ar gas flow than the one in atmosphere welding, arc and weld pool were protected perfectly in hyperbaric air.To apply the automatic welding machine in the chamber, cables airproof and viewing systems adaptability have been solved specially, further more, voltage was replaced by arc length as a key control parameter to eliminate power cable effects.16Mn steel plate welding trials have shown that, although the operation parameters to realize one-side welding with back formation vary obviously in different air pressures and different positions, sound joints still can be obtained with pulsed current.