Duocaidima leadzinc ore deposit, located at the Yushu area of Qinghai, is tectonically situated in the northeastern margin of Tibetan Plateau. Bounded between the Xijir UlanJinshajiang suture zone and BangonghuNujiang suture zone, the deposit belongs to the CuPbZnAg polymetallic mineralization belt in the northern part of the Sanjiang area. Combining with regional geological survey and research status, we carried out CO isotope analysis of carbonatic rock in wall rocks and twostage hydrothermal calcite veins, and S isotope analysis of sulfide minerals and barite. The results are given as follows. The δ13C and δ18O value ranges of calcites in wall rocks are -1.6‰～+3.0‰ and +21.2‰～+27.6‰ respectively, suggesting that calcites belong to normal marine carbonate deposition, with C and O deriving from seawater. The δ13C and δ18O values of calcite veins are -1.5‰～+2.1‰ and +15.2‰～+20.3‰ respectively, while the C derived from the dissolution of carbonate rocks, and the 18O depleted during isotopic exchange of waterrock reaction. The δ34S values of barite range from +12.3‰ to +15.7‰ and δ34S values of galena, sphalerite and pyrite all range from -8.2‰ to +5.7‰ with a peak of -2.0‰～-3.0‰, which reflects a feature of rich light sulfur, and sulfur was derived from extraction of the thermal brine in basin, thermal decomposition and reduction of the organic matters and fractionation of lowvalence sulfur. A relative wide range of δ34S reflects the interaction of oreforming material with wall rocks during the flowing of hydrothermal fluids in the basin. Sedimentary and biogenetic sulfur in organic matterrich strata in the basin may provide partial sulfur source for the mineralization.