Abstract: The welding arc in PAW effected by activated flux was studied, and the relationship between the welding arc voltage and activated flux was also studied.In activated flux PAW, the welding arc temperature field was measured by the infrared sensing and computer image technique. The distribution models of heat flow density of welding arc in activated flux PAW were developed.The results show that the activated flux PAW arc is contractive;the arc tail is disappeared; the efflux plasma is increasing; the force of penetration is strengthened;the arc voltage is high;the welding arc temperature distribution in activated flux PAW is compact; the outline of the welding arc temperature field is narrow;the range of the welding arc temperature distribution is concentrated; the welding arc radial temperature gradient is large; the welding arc radial temperature gradient shows normal Gauss distribution. The result shows that there is little difference in mechanical properties between the welded joints with activated flux and that without activated flux.