Abstract: Four kinds of metal cadmium, znic, titanium and chromium were used as the activating fluxes for the A-TIG welding of magnesium alloy and the influence of metal activating fluxes on the weld morphology, the arc shape and the arc voltage has been analyzed. The results indicated that compared with the conventional TIG welding, both znic flux and cadmium flux increased the weld penetration depth, while the chromium flux redcued it and the effect of Ti flux was negligible. It could also be observed that the arc concentrated and the arc voltage increased with both znic and cadmium fluxes, while the variations of the arc and the arc voltage with titanium and chromium fluxes were hardly be observed. The main mechanism that znic and cadmium activating fluxes enhance weld penetration for the A-TIG welding of magnesium alloy may be that these fluxes constrict the currentconducting channel of the arc during the positive period of alternating current, due to the effect of the melting point, the boiling point and the first ionization energy.