Abstract: Activating flux tungsten inert gas (A-TIG) tests were conducted using a self-developed C5 active agent to study the effects of the active agent on the A-TIG weld formation, arc spectrum and arc morphology. At the same time, scanning electron microscope (SEM) was used to observe the morphology of the black residue, and the composition of the black residue after A-TIG welding was analyzed to determine the reasons for the formation of the black residue. The results showed that the active agent helped to increase the arc temperature and penetrative capacity, promote arc ionization, and change the surface tension gradient and the direction of melt pool flow, thus increasing the welding depth. Compared with the weld matrix, oxygen, chromium and titanium elements were more densely distributed in the residue, while other elements were diffusely distributed inside the residue. When observing the microstructure and properties of the welds, it was found that the weld centers were all equiaxial crystals with austenite and ferrite as the main tissues, while the fusion zones of the joints all showed columnar crystals. The average tensile strength of the specimen without residue removal was 675.36 MPa.Compared with the strength of the base metal, the strength was increased by 2%. The hardness curves of the weld and the base metal were staggered, and whether or not the residue was removed had little effect on the hardness of the joint. There was no crack on the surface of the two groups of specimens after bending 180°. The welds welded by A-TIG had good ductility and toughness. In addition, the weld surface of the specimen without residue removal had a concave phenomenon, but the weld width was uniform, and the weld shaping coefficient was 1.97, which could obtain a wide range of weld equiaxial crystals and relatively fine weld microstructure, and had smaller deformation than that of tungsten inert gas (TIG).