Abstract: The effects of a new method of supplying gases in an alternating Titanium alloy TA2 GMAW bead welding were investigated. High-speed camera and hall sensor were used to collect the information of arc shape,droplet transition,current signal and so on,and the morphology of weld cross section was recorded. The results show that the mode of droplet transfer under alternating manner is a mixed mode of fine droplets axial transition(Ar atmosphere) and coarse droplets non-axial transition(He atmosphere); the welding current changes in sin waves over time,and the change frequency is consistent with alternating frequency; compared with conventional protection methods,the new one could produce deeper penetration and wider fusion width.