Abstract: This paper deals with the development of an activating flux for A-TIG welding of stainless steel which is made up of B₂O₃,MnO,Fe₂O₃,Al₂O₃,SiO₂,TiO₂,Cr₂O₃,NaF,etc. The effects of each components of the flux on the welding penetration is investigated. Based on the investigation, the primary elements of the flux are determined and the formulas are derived through orthogonal test. The penetration can be increased more than 2 times with the developed flux. The 8mm thick plates of stainless steel can be completely penerrated in a single pass without groove.The welded joint is satisfactory in microstructure,chemical composition,mechanical property and anti-intergranular conosion property.