Abstract: The Shewushan gold deposit is the largest gold deposit in the southeastern Hubei area, Previous scientific research in this area has insufficiently studied the nature of the ore - forming fluids of the primary gold deposit. Through laser Raman analysis of inclusions, fluid inclusion temperature measurement, and pyrite S - isotope determination, this paper has identified the nature, composition, and source of the ore - forming fluids in this area, aiming to deepen the metallogenic theory in this area. The results show that the ore - forming fluids in this area are of the H₂O - NaCl system, commonly containing CO₂ and a small amount of CH₄. The fluid temperature and salinity gradually decrease from the pre - ore - forming stage to the post - ore - forming stage, indicating that the participation of meteoric water leads to the dilution and cooling of the hydrothermal system. The δ³⁴S values of pyrite mainly range from - 9.5‰ to - 5.1‰, which are significantly different from the sedimentary sulfur in the Cambrian - Ordovician strata in southern Hubei, suggesting that the deep magmatic sulfur is the main source, with a small amount of sedimentary sulfur mixed in. The study believes that the genetic model of this deposit is the mixing of deep - seated magma and basin sedimentary fluids. They interact with meteoric water and carbonate wall - rocks in the fracture zone. Along with the decrease in temperature and pressure, salinity dilution, pH value change, and the sulfate reduction process mediated by organic matter, the precipitation of gold is triggered.