A-TIG welding for titanium alloy was carried out to study effect of surface activating flux on welding penetration. Halides(CaF2, ZnF2 and MnCl2), Oxides(SiO2, TiO2 and V2O5) and elemental Te were served as fluxes. It is found that the three kinds of experimental halides can improve welding penetration, especially the welding penetration for MnCl2 reaches two times of that of conventional TIG welding. The three kinds of oxides have little effect on weld forming. Elemental Te can curiously increase welding penetration and decrease weld width. It is believed, arc constriction is the main mechanism of halides improving welding penetration of A-TIG welding for titanium alloy, but not for elemental Te.