Abstract: Based on investigation into the differences of arc shape, arc voltage and weld geometry between conventional TIG welding and activated TIG welding with activating flux SiO₂, the effect of activating flux SiO₂ on arc plasma shape, electric field intensity of arc space, arc temperature, arc current density and arc force were analyzed.The results indicated the activating flux SiO₂ makes arc plasma contractive, heating zone and arc force of arc plasma much more concentrated.Meanwhile, the activating flux SiO₂ drastically increases the electric field intensity, temperature and current density in arc space.As a result, theweld geometry is changed, but there are no great changes present in width.