The diversity of the landslide dam structure will result in the difference in the dam body’s seepage. In this paper, based on two kinds of soil bodies of different particle gradations, fourteen groups of structures of the landslide dam are designed to generalize different seepage developments and breaking processes. The study shows that the saturation and seepage evolution characteristics of the landslide dam's seepage have a considerable influence on the landslide dam’s breaking characteristics. An empirical formula is fitted according to the time-seepage degree curve of the landslide dams of different breaking processes to predict the breaking forms of the landslide dams before the dam break. During the water storage process of the landslide dam, the seepage's saturation process inside the dam body reduces the stability of the landslide dam, thus affecting the evolution of the failure process after it has started. In the experiment, it is found that the growth rate of the seepage degree of the landslide dam is inversely proportional to the growth rate of the dam breach area. Although the internal penetration of landslide dams is usually undervalued, the result verifies that the study on the seepage process before the breaking of landslide dam is conductive for further understanding the breaking mechanism of the landslide dam.

River blockage and dam break usually occur in mountainous areas with many valleys, and are frequent and extremely harmful natural disasters. With the construction of infrastructures in mountainous areas, the demand for disaster prevention and control has been further increased. Based on an innovative flume model for simulating whole process of river blockage and dam break, the present study carried out eight groups tests under different inflow rates. In the analysis, the whole process of river blockage and dam break was divided into four stages: ESBA (Early stage of blockage), LSBA (Late stage of blockage), ESBK (Early stage of breaking) and LSBK (Late stage of breaking). By analyzing the relationship between Qin and Qmax, it is found that Qmax shows an overall trend of increase with the increase of Qin while some contrarily decreasing Qmax cases exist when Qin slightly increases. The cases of irregularities may come from the inflow condition impact and randomness during the dam formation process. In addition, the slope of the curve Qin–Qmax/Qin parameter shows a decreasing trend with the increase in the median particle size of the soil. The present study proposes a new method for model experiments, providing new ideas for subsequent model experiments. Furthermore, these conclusions can provide reference for disaster prevention and mitigation in mountainous areas.