Abstract: The foundation failure of a dam on the eastern margin of the Tibetan Plateau during seepage and chemical processes is studied. By using Cl^- tracing, temperature-conductivity tracing and artificial tracing techniques, it is determined that there is leakage through the non-closed concrete cut-off wall, where the reservoir water leaks through the dam foundation, and excretes through the filter layer after the dam area. The acid dissolution experiment and X-ray fluorescence analysis show that the precipitated white particles on the surface after the dam are mainly composited of CaCO₃. Combined with the chemical reaction process. It is confirmed that the precipitation comes from the cement of cut-off wall. The CO₂ dissolved in the leakage water reacting with Ca(OH)₂ in the cement can generate soluble Ca(HCO₃)₂, which is taken to the surface by the leakage water and decomposed to CaCO₃ at normal temperature. Through the measurement and analysis of CO₂ content in surface water, it is found that CO₂ in the water-rock reaction has other sources except atmospheric precipitation. Considering the local geologic structure, it is inferred that CO₂ mainly from the deep carbon pool enters the groundwater and reservoir water through the fault zones, and participates in the water-rock reaction. This results in a faster erosion of the dam. The chemical erosion of the dam and hydraulic structures will be greatly enhanced if the deep CO₂ enters the groundwater and participates in the seepage process.