Abstract: A-TIG welding experiments were conducted by using five species of single-component activating fluxes, including SiO₂, TiO₂, CaF₂, Cr₂O₃, BaCl₂ and complex formulation YG304.The spectrum in A-TIG welding process is tested by spectrometer.The distribution law of flux element in arc space is analyzed.The experimental results indicate that the above activating fluxes have different effects on weld penetration.The most remarkable increasing is obtained when the flux is YG304.The spectral lines of argon atom and aluminum atom are the main spectral lines of the A-TIG welding arc.Different cross-spectrum distribution of arc is presented with different fluxes.The increasing of penetration may be attributed to the recombination of positive ions such as Si⁴⁺, Ti⁴⁺, Cr³⁺ and electron that generates from Ar arc, thus raise the arc temperature and arc force, and ultimately the weld penetration increases.The effect of increased penetration is due to various physical properties of positive ion.