This paper studies the source and characteristics of the ore-forming fluids in the Mengya’a Pb-Zn deposit of oft-com:office:smarttags" />Tibet and identifies the genetic type of deposit by studying the typical deposit of this area. It analyzes the altered limestone in the surrounding area, the carbon and oxygen isotopes of hydrothermal calcite and the hydrogen and oxygen isotopes of quartz formed in different mineralization periods, studies the fluid inclusions petrographically, and measures their temperatures and salinity. The result shows that in the early post-mineralization stage, the ore-forming fluids were mainly in the form of magmatic water, while in the later stage, they were mixed with plentiful meteoric water.