In this study, the variation in the expansion displacement of concrete samples with different water-cement ratios under five corrosion solutions (single sulfate salt and coupled sulfate-chloride salt) is explored. The expansion displacement evolution of these concrete samples under sulfate corrosion (single salt corrosion) and sulfate-chloride corrosion (double salt corrosion) is comprehensively examined. The results reveal that the continuous accumulation of corrosion damage eventually manifests in the form of expansion displacement. Based on the experimental results and the chemical reaction rate equation of the delayed ettringite formation and Friedel’s salt generation, an evolution model of expansion force is established. According to this model and the Weibull distribution law of damage, a expansion displacement mechanics model is proposed to predict the expansion displacement behavior of concrete under sulfate corrosion as well as combined sulfate-chloride corrosion.