The Fangyangshan Cu-Pb-Zn polymetallic deposit in Zhenkang County of western Yunnan Province is the first copper-rich deposit recently discovered in the south of Baoshan block. Fluid inclusions and C-O isotopes were studied in order to reveal the source of ore-forming fluid and the genesis of the deposit. The study shows that stage Ⅱ is dominated by liquid-rich inclusions, whose homogenization temperatures range from 240 to 300℃ and salinities from 8.0% to 18.0%. Stage Ⅲ is characterized by CO₂-rich and daughter minerals-bearing fluid inclusions with homogenization temperatures and salinities both showing two peaks of concentration. Their homogenization temperatures range from 360 to 400℃ with salinities from 16.0% to 24.0%, and temperatures from 240 to 320℃ with salinities from 4.0% to 14.0% respectively. Stage Ⅳ is mainly characterized by liquid-rich and pure-liquid inclusions, whose homogenization temperatures range from 220 to 340℃ and salinities range from 8.0% to 14.0%. The values of δ¹³C_V-PDB and δ¹⁸O_V-SMOW in different stages are plotted in the range of -5.88‰ to -2.37‰ and 8.18‰ to 12.79‰ respectively, indicating that ore-forming fluid of the Fangyangshan deposit was sourced from magmatic hydrothermal solution, with its migration process influenced by the dissolution of wall rocks. According to the above studies, the authors hold that the ore-forming fluid in stage Ⅱ and stage Ⅲ of the Fangyangshan deposit mainly came from the medium-high temperature and salinity and CO₂-rich magmatic hydrothermal solution formed by continental collision, and the ore-forming fluid was influenced by medium-low temperature and low salinity meteoric water in late stage Ⅲ and stage Ⅳ. The authors hold that the Fangyangshan Cu-Pb-Zn polymetallic deposit is a middle-high temperature hypothermal deposit which is controlled by the structure. It is also inferred that skarn type orebodies might be found in the deep part of the mining area.