Pure tungsten electrode is the earliest to be used in TIG welding. It contains tungsten content minimum 99.5%, without other impurities. It is only as welding electrode under the condition of AC or resistance welding electrode. It can clean surface of base metal, welded ball became tapering when heating. This shape provides a good and balanced wave form for AC welding; pure tungsten electrode has a very electron output, low vapor pressure, low resistance, good conductivity, thermal expansion, high elastic modulus bright. Therefore, the arc is stable at low current, and aluminum, magnesium and other metals can be welded at the current below 5A. But the emission of electron demands high voltage and high no-load voltage of welding machine. The tungsten electrode is burned apparently if it works in the high current for a long time. The end may drop into molten pool after melting, which will bring the tungsten into the welding gap.