Abstract: Measurement and analysis have been made for Ar-He gases tungsten welding arc equipped with copper anode and TIG welding gun cooled by water at welding current from 80A to 400 A. The static characters, arc shape and thermal power of the anode and cathode are measured and discussed for different Ar-He gas ratio. The results show that the arc voltage and the proportion of the thermal power in anode increases obviously while the proportion of thermal power in cathode decreases as the ratio of He increases, especially when the content of He reaches 80% or higher. Medium and thick copper plate can be welded by TIG welding. The ideal weld shape and depth can be achieved by increasing the He ratio in the mixture gas and increasing welding current without preheating the work pieces.