Abstract: Most seepage safety analyses for dams focus on the evaluation of stable seepage field, infiltration line and seepage flow. However, under drought-flood abrupt alternation, the soil surface becomes cracked, making it too complicated to conduct a routine seepage analysis. The seepage characteristics of an inclined wall dam under the drought-flood abrupt alternation are studied using a large-scale physical model. The results show that after drought, the permeability coefficient of clay with low crack development is smaller than the saturated permeability, but for the cracked areas with high permeability, the permeability coefficients are much larger than the saturated permeability. As the water level rises, the cracks can heal themselves, but this healing is superficial, and the soil can no longer return to its pre-drought state. After crack healing, the integrity of the dam slope is much less than that of its original state. In addition, the formation of cracks increases the porosity of the soil and changes its permeability, which permanently weakens the anti-seepage performance of the clay soil. The seepage flow behaviors of the inclined wall dam under fluctuating drought-flood conditions are evaluated, and the results can be used to monitor and protect the weak parts of seepage dams in practical projects.