Abstract: The interaction between welding wire and arc (wire-arc) is the key factor to determine the welding quality of hollow tungsten arc welding. Firstly, the shape of hollow tungsten electrode arc and solid tungsten electrode arc, and their influence on the weld forming characteristics are observed and analyzed by high-speed camera. Then the stress model of fuse process is constructed, the dynamic characteristics of droplet formation and transition process in coaxial wire filling welding are systematically analyzed. The research results show that the surface irradiation area of hollow tungsten electrode is larger than that of solid tungsten electrode, and the weld formation is stable under the high welding current. At the stage of droplet formation, the droplet at the end of the welding wire is in static equilibrium, and it cannot spontaneously transition from the end of the welding wire to the molten pool under the action of large surface tension. In droplet transition stage, part of the welding current flows through the welding wire, producing electromagnetic shrinkage force, causing the droplet swing between the welding wire and the molten pool.