Abstract: The Mengnuo Pb-Zn deposit is a large Pb-Zn one in the Pb-Zn-Cu-Fe-Hg-Sb-As-Au metallogenic belt of Baoshan (block). There are different views on the genesis of the deposit, such as sedimentary-reworked type, exhalative sedimentary type (SEDEX) and hydrothermal type deposit (MVT). In this paper, the fluid inclusions of calcite, quartz, barite and sphalerite in Mengnuo lead-zinc deposit are studied to explore the source of the ore-forming fluid and the genesis of the deposit. The results show that the homogenization temperature of the whole metallogenic period of the deposit obeys the normal distribution, and the mode is 170 ～ 280 ℃, which is medium and low temperature. The salinity of the ore-forming fluid is 4.03% ～ 12.73% NaCl, which belongs to the low salinity unsaturated ore-forming fluid. The fluid density of the whole metallogenic period is mainly 0.778～0.978 g/cm³, which shows medium density characteristics. The ore-forming fluid is low-salinity and medium-density one with CO₂ and H₂O as the main components. Combined with the study of geological characteristics and isotopic geochemical characteristics of the deposit, it is considered that the Mengnuo lead-zinc deposit should be a medium-low temperature hydrothermal lead-zinc deposit related to intrusive magmatic geology.