The bond property of the interface between carbon fiber reinforced polymer (CFRP) and clay brick is the key of external CFRP reinforcement technology. In order to understand the degradation law of the bond property of the CFRP-clay brick interface under sulfate erosion, a single shear test was carried out on the specimens strengthened under different sulfate drying and wetting cycles. The results show that the influence of sulfate erosion on the properties of CFRP sheet and impregnating glue is not obvious, but it has a great influence on the bond properties of CFRP-clay brick interface. The shear stress and bearing capacity of the CFRP-clay brick interface increase slightly first and then decrease obviously with the increase of drying and wetting cycles. On the basis of the experiment and the existing theory, the bond slip model of the CFRP-clay brick interface under the action of sulfate drying and wetting cycles is proposed. The model can well reflect the bond property degradation law of the CFRP-clay brick interface by comparing with the experimental value. Based on ABAQUS software, the cohesive force constitutive model was used to simulate the mechanical behavior of the interface. The results show that the cohesive force model can well simulate the nonlinear mechanical behavior of the interface, and the numerical simulation values are in good agreement with the experimental values.