Abstract: Two-TIG activating arc welding process was proposed. Two TIG welding guns were used in a front-to-back arrangement, current of the front welding gun was less than that of the back welding gun and the front welding gun made the arc activating by being mixed with minor O2. Welding procedure test of 5 mm thick SUS304 austenitic stainless steel plate was carried out. The results showed that compared to traditional TIG welding under the same conditions, penetration of two-TIG activating arc welding significantly increased, and surface of the weld was well formed. With the increase of O2 flow, penetration first increased and then decreased, while weld width first decreased and then increased. At the same welding current, as the back welding gun’s current increased and the front welding gun’s current decreased, penetration first increased and then decreased, and weld width continued to increase. With the increase of arc length, penetration first increased and then decreased, and weld width gradually increased. When the tungsten electrode spacing increased from 3 mm, penetration gradually decreased, while weld width increased. However, with the increase of welding speed, both penetration and weld width decreased. The mixing of O2 had no significant effect on microstructure of the weld. Compared to the parent, impact toughness of the weld slightly decreased. This method could realize deep penetration welding at higher welding speed than the common TIG welding.Highlights: Two-TIG activating arc welding was put forward, two independent welding guns were arranged front to back in the plane of welding direction, and welding current of the front welding gun was less than that of the back welding gun. Ar+O2 protective gas was used for the front welding gun, while pure Ar protective gas was used for the back gun, which made the arc activating. At the welding speed higher than that of traditional TIG, penetration significantly increased and 5 mm thick stainless steel plate could be fully welded. Defects such as humping and edge cutting could be eliminated by high speed welding and welding productivity was significantly increased.