A three-dimensional seepage field analysis of the dam was carried out using the finite element numerical simulation, by taking the example of a 110 m-high asphalt concrete core rockfill dam. The research focuses on investigating the influence mechanism of different depths, lengths, and positions of cracks in the bottom gallery of the concrete faceplate dam on the dam’s seepage characteristics. The simulation results reveal that superficial cracks in gallery have little effect on the seepage field of dam, while the emergence of penetrating cracks at the top of the gallery significantly alters the distribution of the nearby seepage field and substantially increases the dam’s seepage volume. On the other hand, cracks at the bottom of the gallery have a relatively minor impact on the seepage volume. In regions where the tensile stress in the gallery exceeds the concrete’s tensile strength, multiple penetrating cracks tend to concentrate, leading to a rapid surge in seepage volume. This also triggers an increase in the permeability gradient within the strataand the transitional zone Ⅰ, warranting close attention.