Abstract: For activating TIG welding of aluminum alloys,including A-TIG welding,FB-TIG welding and FZ-TIG welding,the analysis of chemical reaction between the activating fluxes and the weld pool metal has great significance to certain the fea-sibility of these welding processes and instruct the developments of activating fluxes.Through the XRD analysis of weld surface slag,the chemical reaction thermodynamics was calculated based on functional determinant of Gibbs'Free Energy,and the chemi-cal reaction on welding pool was analyzed.It is found that,for the FZ-TIG welding,with multi-component flux FZ108 developed by authors as central region flux and SiO₂ as outer region flux,the endothermic reactions between flux FZ108 and the welding pool metal can constrict the arc and increase weld penetration.For the A-TIG welding with flux FZ108,the few absorbed heat or the released heat of the chemical reactions has small influence on the arc.For the FB-TIG welding with flux SiO₂,the chemical re-action between the flux and the weld pool metal and its surface oxide film does not happen,and the arc is not affected through these chemical reactions.