<p>Cold metal transfer (CMT)-wire arc additive manufacturing (WAAM) has been widely utilized in the production of large stainless steel components; however, with the increase in additive height, the thermal input and heat accumulation inherent in the CMT-WAAM process can adversely affect the microstructure and properties of austenitic stainless steel. In this study, a liquid nitrogen rapid cooling technique was proposed, where the microstructural changes of austenitic stainless steel walls at different positions (top, middle, and bottom) under varying liquid nitrogen flow rates were analyzed using metallographic microscopy, scanning electron microscopy (SEM), and x-ray diffraction (XRD). Subsequently, Vickers hardness tests and room temperature tensile tests were conducted to investigate the mechanical properties of the walls, and the trends and mechanisms of these changes were discussed. The results showed that as the liquid nitrogen flow rate increased, the strength of the <i>γ</i>-austenite phase decreased, while the strength of the <i>δ</i>-ferrite phase increased. Skeletal ferrite in the <i>δ</i>-ferrite phase gradually transformed into lath-like ferrite, accompanied by the formation of fine equiaxed grains, and coarse columnar grains transitioned into fine columnar grains with additional fine needle-like ferrite appearing. With increasing liquid nitrogen flow, the microhardness, tensile strength, and elongation of the additive walls exhibited a gradual upward trend. This study provides a novel process optimization method to address challenges such as high thermal input, severe heat accumulation in large component production, and low production efficiency in arc additive manufacturing.</p>