Abstract: A-TIG welding is a novel and efficient method of welding. It is characterised with higher penetration than ordinary TIG welding,less heat-affected zone,narrow weld,and less amount of deformation. Besides,it has a high welding efficiency and so on. The application of A-TIG welding in all-position welding for the mild steel pipe was studied. After the activating fluxes was deposed on the metal surface by a brusher before welding,the forced state of the weld pool at different area of the pipe was analyzed during the weld process,and the regulation of welding with activating fluxes for tube was provided. All-position welding machine was used in pipe welding. The full penetration can be got in a single pass without groove preparation for the mild steel pipes of 6 mm thickness,compared with 2 mm in conventional TIG welding process. By this process,the application range of the all-position welding machine can be extended. The efficiency of pipe welding has been improved.