Abstract: In order to investigate the mechanism of seepage failure of landslide dam, the development mechanism of the whole process from seepage failure to overtopping is studied from three aspects: material gradation, initial seepage channel location and dam compactness, by carrying out physical simulation of seepage failure of landslide dam. The research results show that: the expansion of the seepage channel is slow in the early stage of seepage failure, which prolongs the dam failure time to a certain extent; as the seepage channel continues to expand, the scouring effect of the infiltration flow on the soil of the seepage channel is gradually strong, resulting in cracks and intermittent collapse of the soil above the channel; the collapsed soil is easy to be scoured downstream by the flow because it is loose, and the development of the seepage channel is fast at this stage, and during this stage, the development of seepage channels is fast, mainly intermittent expansion, and in a relatively short period of time, the mode of dam failure changes from seepage failure to overtopping, the flow rate reaches a rapid peak and then gradually decreases, and there is a small increase in the flow rate caused by intermittent collapse of the slope of the breach during the process of gradual reduction of the flow rate; the location of the initial seepage channel has a significant impact on the peak flow rate of the dam breach, where the horizontal location (the middle of the dam or the shoulder) has a more obvious impact than the vertical location. The closer the initial seepage channel is to the shoulder of the dam, the slower the development of the breach and the smaller the residual breach width. The research findings can serve as a guide for creating a mathematical model for seepage failures of barrier dams. Additionally, the results can be used to select appropriate risk prevention and treatment plans for seepage failures in barrier dams.