Abstract: For AZ31B magnesium alloy materials, five kinds of single oxides MgO, Cr₂O₃, CaO, TiO₂,MnO₂ were used as the activating fluxes.The welding penetration, microstructures, phase composition and mechanical properties of welded joints without and with single oxide TiO₂ and the composite oxide were compared.The results of experiments showed that welding penetration of compound fluxes is 2.5 times than conventional tungsten inert-gas welding, also deeper than that with single flux.The crystal grain of the composite fluxes is smaller than that of single TiO₂ flux, and the tensile strength of the composite fluxes sample is superior to single TiO₂ flux sample. The activating element was added into weld that improve the phase composition of compound fluxes, which avoid the formation of the low-melting point magnesium-aluminum phase in the welded joint.