Degassing of CO₂ from the solid Earth significantly influences the surface carbon cycle. In addition to volcanic activity, various types of active faults in nonvolcanic regions serve as crucial pathways for the migration and release of deep carbon to the surface. The continental collision zone, exemplified by the Tibetan Plateau and its surroundings, is one of the most tectonically active regions in the world. However, general research on deep carbon origins and outgassing rates of active faults remains limited. Southwestern Yunnan lies on the southeastern margin of the Tibetan Plateau and is characterized by a network of left- and right-lateral strike-slip faults. The area experiences frequent seismic events and abundant hydrothermal activity. The hydrochemical, hydrogen, and oxygen isotope compositions of 12 hot springs in the Lancang fault zone of southwestern Yunnan indicate that the hot spring water exhibits an HCO₃-Na type composition, primarily sourced from atmospheric precipitation, and shows no significant contamination from magmatic or metamorphic fluids. During subsurface fluid circulation, it undergoes mineral dissolution and ion exchange reactions with the surrounding rock minerals, which are influenced by the dissolution of minerals, such as silicates, carbonates, and evaporites. A mass balance model based on the concentrations of Dissolved Inorganic Carbon (DIC) and its carbon isotopic compositions shows that the contribution of deep carbon to DIC is approximately 46.9%~78.0%, which, together with the flow rates of thermal spring water, yield an estimated deep carbon outflux of approximately 440 t/a for the Lancang fault zone. The total deep carbon outflux of the thermal springs in southwestern Yunnan was estimated to be approximately 3×10⁴ t/a. The higher deep carbon fluxes and contributions observed in the thermal springs near the Lancang fault zone demonstrate the predominant influence of strike-slip faults on the origin and release of deeply sourced carbon-bearing fluids. Considering the tectonic context of the strike-slip movement, we suggest that the deformation and fracturing of deep rocks within the Lancang fault zone facilitated the migration of a significant volume of metamorphic CO₂ and a minor portion of mantle-derived carbon to the shallow geothermal system. This process might have resulted in the formation of a reservoir enriched in CO₂ fluids that could transfer carbon to the surface. These findings provide observational evidence that enhances our understanding of the mechanisms of deep carbon release in the active fault zones of southwestern Yunnan.