Abstract: The reaction path and the reaction mechanism of water gas shift reaction (WGSR) on the Cu-Pt-Au catalyst surface were investigated using density functional theory (DFT). The stability and electron activity of binary and ternary catalysts composed of Cu, Pt and Au were studied. The synergistic effect of Pt-Au catalyst in binary alloy is better, and the binding energy of Pt₃-Au(111) surface is 77.15 eV, and energy level of d-band center is -3.18 eV. When the Pt₃-Au(111) surface continues to be doped with Cu, the binding energy of Cu₃-Pt₃-Au(111) is 77. 99 eV and the center of d-band is -3. 05 eV according to the binding energy and density of stares. The energy barrier of CO oxidization is 4.84 eV in the redox mechanism. The reaction is not easy to follow the redox mechanism. Moreover, the two intermediates CHO and COOH are competitive, the energy barrier of forming COOH is larger than that of forming CHO, the reaction is more easily carried out according to the formic acid mechanism.