Abstract: Occurred in the Lower Devonian skarn, the Youmapo tungsten-molybdenum deposit is a large-size recently evaluated skarn type deposit in the Bobai-Cenxi W-Mo-Pb-Sn-Au-Ag metallogenic belt, southeast Guangxi.Four stages of skarn-type ores have been distinguished, i.e., Stage Ⅰ-dry skarn stage, Stage Ⅱ-wet skarn stage, Stage Ⅲ-quartz and sulfide stage, and Stage Ⅳ-carbonate and fluorite stage.In addition, the Stage Ⅱ and the Stage Ⅲ are main metallogenic stages.In order to explore the characteristics of ore-forming fluid in mineralization, the microthermometry of fluid inclusions has been used to research the nature of the ore-forming fluids in the main ore-forming stage.Results indicate that the homogenization temperatures of the fluid inclusions in stage Ⅱ and Ⅲ mainly vary from 280 to 340℃ and from 260 to 320℃, whereas their salinities mainly range from 3.33% to 5.94% and from 5.05% to 9.99%, respectively.The ore-forming fluid in this deposit has the characteristics of medium to high homogenization temperatures and low salinity.Boiling and mixing have occurred during the mineralization.The ore deposit is a medium to high magmatic hydrothermal replacement filling type deposit, and the mineralization in the area was related to late Yanshanian Youmapo pluton.