Yanshan gold deposit is located within the Daliuhang gold field of the Qixia- Penglai metallogenic belt in the Jiaodong Peninsula. It is a typical quartz vein type gold deposit with orebodies occurring in the Mesozoic granite rocks, controlled by faults and present in lenticular or vein forms. Hydrothermal mineralization can be divided into four stages: potash feldspar- biotite- quartz stage, pyrite- quartz stage, polymetallic sulfide stage and quartz- calcite stage, with stages 2 and 3 as the main mineralization stages. The characteristics of the fluid inclusions from gold ores show that they can be divided into five types: two- phase vapor inclusions (Ⅰ), liquid inclusions (Ⅱ), liquid CO2- rich inclusions (Ⅲ), vapor inclusions (Ⅳ), and high saline halite- bearing inclusions (Ⅴ). The results of Laser Raman spectra study show that the composition of volatile phases is mainly CO2, less CH4, N2, H2S, organic matter and so on. The ore- forming fluid belongs to NaCl- H2O- CO2 brine system. The homogenization temperatures range from 167 ~393℃, the peaks from 260~320℃, the salinities from 2. 04％~11. 51％NaCleq. NaCland the density range from 0. 54~ 0. 91g/cm3. These evidences from the fluid inclusions suggest that the ore- forming fluid was medium- low temperature, medium- low salinity and medium- low density. The values of δ18OH2O and δD are 2. 9‰～6. 6‰ and -82. 9‰～-70. 5‰ respectively. The composition of the oxygen and hydrogen isotope demonstrates that the ore- forming fluid is derived from mainly magmatic water and mixed with parts of meteorological water. On the basis of the geological and fluid inclusion features, we conclude that the Yanshan deposit is a medium- low thermal gold deposit.