The infiltration and degradation of domestic contaminants have a substantial influence on the mechanical properties of soil. Sucrose is one of the oligosaccharide contaminants with high content and is prone to degradation in domestic-source contaminants. In this study, a series of tests were conducted to investigate the changes in the mechanical properties of clayey soil during the sucrose degradation process. First, in different concentrations of sucrose-contaminated soil, the organic matter content during the sucrose degradation process was measured to analyze its degradation characteristics. During the degradation process, the unconfined compressive strength and compression coefficient of the soil were measured to analyze the changes in its mechanical properties. Finally, the changes in the permeability coefficient and microstructure of the soil were analyzed in depth. The findings indicated that the degradation of sucrose and the associated alterations in the mechanical properties of contaminated soil were concentration-dependent. The effect mechanism involved the formation of organic-clay flocs during the early stages of degradation and the alkaline oxides' dissolution in the later stages. These findings contribute to a deeper understanding of the impact of domestic-source pollution on soil and provide references for the reinforcement of contaminated soil.