Abstract: In recent years, the Chagandells molybdenum deposit is the the most important outcome of prospecting molybdenum deposit in the central and western part of Inner Mongolia.The study on fluid inclusions of this deposit has been carried out in this paper.The results show that, the gas-liquid two-phase inclusions of H₂O-NaCl-CO₂ system were developed within the molybdenite-quartz-sericite veinlets in the main mineralization stage, with a small number of daughter mineral-phase inclusions; and the gas-liquid two-phase inclusions of H₂O-CO₂ system were occurred within the molybdenite-quartz veinlets during the late mineralization stage, with little gas-phase inclusions.The test results show that the main mineralization stage belongs to high temperature and low salinity mineralization, while the late mineralization stage was formed in low temperature and low salinity conditions, with the addition of meteoric water in late stage.The mineralization of this deposit might be related to the mixing between high-temperature silicon-rich hydrothermal and atmospheric water.The changes of temperature, pressure, pH and Eh promote the precipitation of ore-bearing minerals in the fluid to fill and crystallize as the molybdenum deposit.The H-O isotope of fluid inclusions indicates that the low hydrogen isotope values were caused by the mixing between magmatic hydrothermal and meteoric water, as well as affected by tectonic stress.When the hydrothermal migrated into the fissures of surrounding rock, the physical and chemical conditions were changed, and the molybdenite was filled into these fissures to form the molybdenum deposit.S isotope studies show that they were sourced from crustal sulfur, and the sulfur isotope values are close to the sulfur values of acid rock, thus they might be derived from the mixture of remelting hydrothermal magmatic rocks and atmospheric water.Finally, the genesis type of this deposit may be belonged to the late magmatic hydrothermal quartz vein filled-type deposit.