Abstract: For the gas pool coupled activating TIG (GPCA-TIG) welding with outer mixing shielding gas of nitrogen and oxygen, by changing the relative position of the outer and inner nozzles of welding torch, the effect of coupling degree between the outer shielding gas and welding pool surface on nitrogen-oxygen content in the weld appearance, microstructure and properties. The results show that the gas pool coupled activating TIG weld was narrow and deep when nitrogen was introduced in conjunction with oxygen. The low temperature impact toughness of weld was 7.5% higher than that of parent metal and weld made by traditional TIG welding, while the tensile strength and yield strength of weld by GPCA-TIG was lower than those of parent metal. The grains in the weld were fine, and a small amount of ferrites distributed in the austenite grain boundaries. The nitrogen-oxygen content in the weld could be finely adjusted through changing the relative position of outer and inner nozzles in GPCA-TIG welding.