Dajishan tungsten deposit, located in the Nanling metallogenic province of tungsten and tin, is a famous large tungsten deposit in China. This paper studied No. 2513 vein in the Dajishan tungsten veintype deposit using facieology and microthermometry, and then discusses the evolution and depth of oreforming fluid. The facieology study on the fluid inclusions reveals a variety of fluid inclusions: aqueous inclusions, bearing CO2/CH4 three phases fluid inclusions and bearing daughter mineral fluid inclusions.The assemblage of fluid inclusion are quite complex, with different types of fluid inclusions generally overprinted. It is easy to distinguish between primary fluid inclusion and secondary ones based on their different filling characteristics. Primary fluid inclusions consist of bearing CO2/CH4 three phases fluid inclusion or low filling degree aqueous inclusion, while secondary fluid inclusions are high filling degree aqueous inclusion. Microthermometry analysis data indicates that the salinity and homogeneous temperature differ with fluid inclusions types markedly, manifesting a complicated fluid evolution process. TThe dercepitation temperature curves display that there are two initial dercepitation temperatures which correspond to primary and secondary fluid inclusions respectively. The dercepitation temperature of primary fluid inclusions declines from deep to shallow level. The analysis on the components of primary fluid inclusions using confocal Raman microscopy demonstrates that the oreforming fluid is H2ONaCl or H2OCO2CH4NaCl system. According to microthermometry data, it is identified that oreforming fluid evolutions in Dajishan tungsten deposit are composed of cooling, immiscibility and mixing processes. Employing microthermometry data of immiscibility fluid inclusions, following conclusions can be drawn on: a) the oreforming pressure is about 114~132Mpa; and b) the oreforming depth is about 4.6~5.3km.