Abstract: The effect of individual component in active flux on weld formation during the TIG welding of AZ31 magnesium alloy was investigated in this paper.The experimental results show that compared with weld without active flux the weld penetration and weld depth-to-width ratio are greatly increased by applying the active flux of TiO₂、SiO₂、Cr₂O₃、CdCl₂ and CaCl₂ for magnesium alloy.The microstructure of weld made with CdCl₂ didnlt change significantly,but its heat affected zone is wider.The hardness of weld made without active flux is almost the same with that with CdCl₂.As the effect of CdCl₂ is the best for the AZ31magnesium alloy.