The mechanism and activity of the water-gas shift reaction (WGSR) on single-atom alloy Al1/Cu (111) and Cu (111) surfaces were studied using GGA-PBE-D3. Al1/Cu (111) exhibited bifunctional active sites, with the Al site being positively charged and the Cu site negatively charged due to electronic interactions. This led to selective adsorption of H2O and CO. Al1/Cu (111) promoted H2O adsorption and dissociation, reducing the energy barrier to 0.67 eV compared with 1.13 eV on the Cu (111) surface. Meanwhile, Cu served as the active site for H2 formation, which is the rate-determining step, with an energy barrier of 0.95 eV. The Al-O and Cu-C bonds cooperatively increased the interaction strength of O-containing intermediates. Al1/Cu (111) promoted the whole WGSR through cooperativity, reducing the overall apparent activation energy. This work gives insights for the design of single atom alloy (SAA) catalysts with p-p orbital energy level matching, which facilitates orbital interactions between Al and H2O, thus achieving excellent WGSR activity.