The Langcun W-Mo deposit, located in the Zhejiang Province of South China, is a medium-sized porphyry deposit. The ore bodies mainly occur in aplite, granite porphyry, and the contact zone with hornfels of the Nanhua System. Four stages of mineralization are recognized in the Langcun deposit, including the quartz–K-feldspar stage (stage I), quartz–sericite–molybdenite stage (stage II), quartz–chlorite–pyrite stage (stage III), and calcite stage (stage IV). Stages I and II are the main ore-forming stages for wolframite and molybdenite. The petrographic and microthermometric results show that four types of fluid inclusions exist in the Langcun W-Mo deposit, including two-phase liquid-rich fluid inclusions (type LV), three-phase CO₂-rich fluid inclusions (type LC), pure CO₂ fluid inclusions (type C), vapor H₂O inclusions (type V), and multi-phase inclusions with daughter minerals (type LDV). In stage I, the fluid inclusion assemblage is LDV + LV + V, and the LDV and LV fluid inclusions have similar homogenization temperatures (281–387 °C), indicating a boiling fluid inclusions association. In stage II, the fluid inclusion assemblage is LC + C, indicating immiscibility between CO₂ and aqueous fluids. The homogenization temperatures of type LC are in the range of 228–342 °C, and the salinities are in the range of 2.77–5.14 wt.% NaCl equiv. The fluid inclusions in stages III and IV are type LV, with homogenization temperatures in the ranges of 224–275 °C and 200–225 °C, respectively, and salinities in the ranges of 1.74 to 4.96 wt.% NaCl equiv and 1.06 to 3.39 wt.% NaCl equiv, respectively. Hydrogen and oxygen isotopic results indicate that the ore-forming fluids mainly come from magmatic water in the early stage and may have received an input of meteoric water in the late stage, which results in the decrease in the temperature and salinity of ore-forming fluid. Early W-Mo precipitation was induced by CO₂ escape because of decompression, and fluid mixing resulted in Mo precipitation in the later stage.