<p>Traditional cast-wrought processes are limited by high cost and low efficiency in producing complex structural components. Wire arc additive manufacturing (WAAM) has emerged as a viable alternative, offering high deposition rates and cost-effectiveness for fabricating large-scale metallic parts. However, severe heat accumulation during the layer-by-layer deposition process significantly restricts the enhancement of microstructural and mechanical properties. To address this issue, this study proposes a rapid-cooling additive manufacturing method using liquid nitrogen. This method is integrated into a cold metal transfer-based WAAM system. Using ER308L welding wire as the feedstock material and a 304 stainless steel substrate, multi-layer wall structures were fabricated. The effects of liquid nitrogen rapid cooling on deposition efficiency, microstructural evolution, phase composition, grain orientation, and mechanical properties were systematically investigated. Results demonstrate that liquid nitrogen cooling significantly enhances interlayer cooling efficiency and effectively suppresses heat accumulation. The total deposition time for the first six layers was reduced by up to 59%. Microstructural analysis reveals notable grain refinement accompanied by reduced anisotropy, with average austenite and ferrite grain sizes reduced by 16.5 and 15.7%, respectively, and the ferrite content increased from 6 to 10%. Mechanical tests demonstrate that LNC specimens exhibit significantly improved performance, tensile strength and elongation increase by up to 4.9 and 29.2%, while impact toughness improves by over 35%. The performance enhancement is primarily attributed to grain refinement, randomized crystallographic orientation, and the transformation of ferrite from coarse skeletal to refined lath-like morphologies.</p>