Located in northwestern Jiujiang-Ruichang metallogenic area, the Dongleiwan skarn Cu-Mo-Au polymetallic deposit belongs to Jiujiang-Ruichang Cu-Au orefield, which is a component part of the Middle-Lower Yangtze River Cu-Au metallogenic belt and the Daye-Jiujiang metallogenic subzone. Petrographic and microthermometric studies of fluid inclusions in quartz from the main metallogenic phase (quartz-polymetallic sulfide phase) show that the inclusions related to mineralization include mainly four types. Homogenization temperature and salinity w(NaCl_eq) of the ore-forming fluids are concentrated in 210～350℃ and 1%～9% respectively, suggesting medium-high temperature and medium-low salinity. Gases of fluid inclusions mostly contain H₂O and CO₂, followed by N₂, CO and O₂, with a small amount of CH₄ and C₂H₂. Cations of liquid composition mostly consist of Ca²⁺, K⁺ and Na⁺, followed by a small amount of Mg²⁺, while anions are mainly Cl^-, SO₄^2-, followed by NO₃^- and NO₂^-, and the fluid is of the CO₂-H₂O-NaCl-CaCl₂ (KCl) system, with the calculated ion concentrations ranging from 3.1% to 34.5%. Hydrogen-oxygen isotope characteristics show that the δ¹⁸O_H2O values of the ore-forming fluids in the main metallogenic stage are in the range of 0.93‰～5.20‰, and δD_V-SMOW values vary between -81‰ and -64‰, which implies that the ore-forming fluids were mainly derived from magmatic fluids, with the mixture of a small amount of meteoric water. The δ³⁴S_V-CDT‰ values of sulfides range from -2.2‰ to 3.4‰. Lead and rhenium isotopic composition of the ore indicates that the ore-forming materials of the Dongleiwan deposit were derived mostly from the upper mantle, and partially from the crustal materials. The Dongleiwan deposit is a hydrothermal metasomatic skarn type deposit. The folds and fractures of this area provided the migration pathway for mineralization, and magmatic emplacement developed skarn type magmatic fluid subsystems, accompanied by Cu (Mo, Au, etc.) mineralization. These factors eventually led to the formation of the ore deposit.