A three-dimensional(3D) numerical analysis model of stationary activating tungsten inert gas welding(A-TIG welding) arc in interaction with the anode material and the tungsten electrode is presented. According to the method,the distributions of temperature field and velocity field of arc plasma and weld pool,metal vapor concentration and current density in the arc plasma are investigated by solving the Maxwell equations,continuity equation,momentum conservation equation,energy conservation equation and the components of the transport equation. As it is different between A-TIG welding and TIG welding about the flow pattern,the temperature on the anode surface material in A-TIG welding is higher than that in TIG welding, then the metal vapor concentration in A-TIG welding is higher, which causing the temperature contour of A-TIG welding shrinks in the end.With the influence of the metal vapor,temperature contour of A-TIG welding also shrinks for the same reason in TIG welding and it shrinks in a bigger degree than TIG welding. It results that the weld depth decreases about 6% with the impact of metal vapor in A-TIG welding.