Leimengou Mo deposit, located in western Henan province, is one of the classic porphyry Mo deposits in the East Qinling molybdenum belt. The ore-body has a lenticular and stratoid distribution at the inner and outer contact of Leimengou granite porphyry. The ore are characterized by disseminated multistage stockworks. Based on intersection and overprinting relationships among veins throughout the deposit, the molybdenum mineralisation at Leimengou occurred mainly in four hydrothermal stages：（Ⅰ） K-felspar stage; （Ⅱ） Quartz-K-feldspar stage; (Ⅲ) Quartz-molybdenμm stage; (Ⅳ) Qartz-carbonate stage. Three types of fluid inclusions can be distinguished as aqueous (type A), CO2-bearing (type B), and daughter mineral-bearing inclusions (type S). Fluid inclusion microthermometry are combined with geological and textural observations to reconstruct the spatial and temporal evolution of magmatic hydrothermal fluids that forming the Leimengou porphyry Mo deposit. All data demonstrate that the ore-forming fluids of the Leimengou deposits are characterized by medium-high temperature, Medium-low pressure, medium-low salinity, low density fluids as H2O-CO2-NaCl. Hydrogen- oxygen isotopic compositions indicate that magma fluid mixing with meteoric water in various degrees as the main ore forming fluid. Carbon isotope reveals the source of C apparently formed by massive underplating of mafic mantle melts. KHMoO4 and H2MoO4 were the major transporting styles of Mo. water-rock alteration, fluid immiscibility and decreasing of pH were demmed as the key factors controlling the precipitation of Mo and the formation of the ore deposit.