Abstract: The Xiaojiashan tungsten deposit, located at the southern edge of the central area of east Junggar, is one of the metallic deposits in Bogda-Harlik tectonic belt. The structural position of the deposit is in the Harlik double anticline and the tectonic line is mainly EW-striking. The regional strata are mainly composed of 1st and 2nd lithologic member of the 1st Subformation of Middle Devonian Dananhu Formation (D₂d₁¹, D₂d₁²). The mining area has sporadic quartz diorite, moyite and a small number of intermediate-acid granodiorite veins. The orebodies occur in a late Hercian granite intrusion near the metamorphic crystal tuff which consists of the 2nd lithologic member of the 1st Dananhu Subgroup in Middle Devonian (D₂d₁²), whose type is wolframite ores of quartz vein, and wolframite is the main useful metal. Tungsten-bearing quartz veins are divided into gray wolframite-quartz vein and white quartz vein. Quadrupole mass spectrometry reveals that fluid inclusions contain major gas phase contents of CO₂, H₂O and a little variable positive ion component of Ca²⁺. In addition, there is a little variable components of Ar, C₂H₆ in gas phase. Meanwhile, fluid inclusions contain major liquid phase contents of Cl^-, Na⁺ and a little variable positive ion component of Ca²⁺. It can be inferred that the ore-forming fluid of the Xiaojiashan wolframite deposit is characterized by a CO₂-rich, low salinity, and H₂O-CO₂-NaCl system. The origin of the Xiaojiashan wolframite deposit can be considered as a high-temperature hydrothermal quartz vein type deposit controlled by fissure structures. Wolframite-bearing ore veins are distributed mainly over fissure structures. A portion of tungsten must have been sourced from migration and enrichment of mantle hydrothermal intrusion in wall rock and strata. Therefore, W-bearing complexes ore-forming fluid decomposed in the migration process of W, and promoted the precipitation of W in the Xiaojiashan deposit.