Abstract: The effects of gas mixture ratio in hyperbaric environment on pulsed MAG welding splash ratio and the shape of weld pool were analysed. Experimental results showed that more active gas made the weld arc instable, the spatter increase and the welding process extremely unstable in the same condition. In order to obtain the stable welding process and reduce the rate of spatter in hyperbaric environment and then prevent the formation of defects, the ratio of Ar was increased to reduce energy loss. Taking into consideration the influence of the splash ratio, the stability of droplet and the shape of weld pool, experiments results showed that 90%Ar+10%CO₂ gas mixtures in 0.3 MPa can make the best welding quality. The effective control of gas mixture ratio has a significant effect on the stability of pulse MAG welding in hyperbaric environment.