Abstract: In the pulsed TIG welding of thin plates with low current, the stability of welding arc is the key problem. This paper describes our systematical studies of this problem with a photo-spectrum measuring system controlled by a microcomputer and a 100MHz oscilloscope of type V-1050F. Using the photo-spectrum method and analyzing the dynamic characteristics of the arc, the authors have found a method of assessing the arc stability and also the factors affecting the arc stability studies.Certain measures controlling the stability of pulsed TIG welding arc and a new process of high frequency Ar-N₂ arc welding have been proposed.