Abstract: Having been investigated the argon-nitrogen TIG arc by using a microcomputer controlled multi-channel spectral system, high-hcat effect and its mechanism of this TIG arc have been disclosed, so as to find out the difference from Ar-H₂ or Ar-Hc TIG arcs. The test results indicate that the Ar-N₂ TIG arc has proper merits for welding pure copper and ultra-low carbon austcnitic stainless steels.