Abstract: Helium-shielded GTAW is known by its high heat power and hence high prod-uctivity,and is expected to have wide applications.The pattern of helium-shield gas, the shape of helium arc and its electrical characteristics and energy distribution are the important subjects of GTAW technology.The authors observed the helium flow pattern by use of the laser technique,took photographs of the arc-shape during GTAW in the He,Ar or He+Ar mixture atmosphere,and measured the electrical characteristcs and the energy distribution.In the mean time the penetration was also investigated. Experiments indicated that the anode heat energy in helium-shielded GTAW was about two times that of argon-shielded GTAW,resulting in therefore considerably deeper penetration.In view of the fact that no substantial increase of anode heat energy andpenetration can be made by adding helium to argon,the authors constructed a special dual-nozzle in which helium flows in the inner nozzle while argon in the outter. The penetration in this case is close to that of helium-shielded GTAW.