Abstract: Activating TIG(A-TIG) welding has received considerably attentions worldwide since the end of 1990s.Compared with conventional TIG welding A-TIG welding can greatly improve the welding productivity and reduce the welding cost without altering the equipments under the same welding procedure.The effect of activating fluxes with single component on weld form during the TIG welding of stainless steel and titanium alloy is studied in this paper.The experimental results show that compared with weld made without flux the weld bead penetration is greatly increased after applied with flux SiO₂,CaF₂,TiO₂,Cr₂O₃ and NaF for both stainless steel and titanium alloy.When the coating quantity of flux increases,the weld bead penetration increases while the weld bead width decreases.However weld made with flux CaF₂ is worse than welds made with other fluxes for stainless steel,and weld bead width made with flux Cr₂O₃ does not vary significantly compared with weld without flux for titanium alloy.As to the stainless steel the effect of flux SiO₂ is the greatest,and flux CaF₂ is the best for the titanium alloy.The arc constricting and surface tension variation of weld pool are the main mechanisms for the weld penetration increase after applied with activating flux.