Jinchang gold deposit, a cataclastic altered rock-host gold deposit, locates at the northeastern end of Gezhen shear zone of western Hainan. The mineralization in Jinchang can be divided into three stages, based on ore structure and mineral symbiotic combination, while the middle stage is the main stage for Au precipitation. Fluid inclusions petrography study shows that the early and middle stage is rich in CO2 fluid inclusions and the late stage is dominated by aqueous fluid inclusions. The homogenization temperature of each stage is 280~324℃, 211~303℃, 147~259℃while the salinity ranges from 6.20%~9.98%NaCleqv, 1.74%~10.73%NaCleqv, 0.18%~10.11%NaCleqv respectively. The ore-forming fluid is characterized by medium to low temperature and low salinity. Combined with laser Raman spectrum analysis, the ore-forming fluid belongs to H2O-CO2-NaCl type. Through isochore intersection method of immiscible fluid the trapping temperature of the main stage is 330~360℃ while the trapping pressure is 130~150MPa. Comprehensive research shows that fluid boiling and phase separation due to pressure reducing is the main reason for Au precipitation.