Powder molten pool coupled activating TIG welding is a novel efficient welding method. Almost all metals can be welded by selecting corresponding activating flux powders. For AC powder molten pool coupled activating TIG welding arc with MnCl,2, as activating flux, the spectrum of a rc plasma was collected and Boltzmann plot method was used to analyze the variation rule of arc plasma temperature with time. Combined with the variation rule of arc voltage, the effects of MnCl,2, on AC arc were studied based on the comparison with traditional AC TIG arc. The results show that for AC TIG arc, the arc spectral intensity in EN period is higher than that in EP period, the arc voltage and arc temperature in EN period are lower than those in EP period. Because of the introduction of activating flux MnCl,2, the central temperature and arc voltage of AC powder molten pool coupled activating TIG arc are higher than those of traditional AC TIG arc in both EN and EP periods, and the weld penetration of AC powder molten pool coupled activating TIG welding is significantly increased compared with that of traditional AC TIG welding.