Abstract: C1,C2 and C3 were used as activating flux for A-TIG welding of austenitic stainless steel. Effects of different activating flux on the microstructure and mechanical properties of A-TIG welding were analyzed. The results showed that under the same welding parameters,three kinds of activating flux could increase the weld penetration. When C3 was applied,the weld penetration increased the most,which was 3. 11 times of that without C3. Compared with conventional TIG welding,three kinds of activators could contribute to refining the grains near the weld and fusion line,and improve the tensile strength and hardness of the joint. It was found by EDS that the addition of alloy elements in the activating flux changed the element content of the joint,and Al and B elements appeared in the joint. For joints coated with C2 and C3 activating flux,the grain refinement near the weld and fusion line was due to the interaction of grain boundary strengthening and the entry of activating flux elements into the weld,which formed compounds or mesophase during the liquid-phase crystallization process to hinder the dislocation movement and increase nucleation rate. For joints coated with C1 activating flux,Si O₂ slightly caused increase of Si content in the weld through metallurgical reaction,promoted the development of FA solidification mode and the formation of δ phase.