Abstract: This paper deals with the development of an activating flux made of SiO₂, TiO₂, Cr₂O₃, halide etc. for the GTAW of low carbon steel. The effects of each component of the flux on the welding penetration is investigated. Based on the investigation, a proper formula of multi component activating flux is obtained with which the weld penetration of low carbon steel increases remarkably and the 12mm plates could be welded well without groove.