<p>Landslide dams typically exhibit loose material composition and irregular shapes, making them highly susceptible to seepage. Most studies focus on the effects of seepage under the influence of a single factor on the dam failure process. However, seepage development is often driven by multiple interacting factors, which should be carefully considered. In this study, 54 flume experiments were conducted under various conditions (dam heights, downstream slope angles, inflow rates, soil grain size distribution, and seepage intensity) to investigate changes in failure process and characteristics in landslide dams: (1) As the influence of seepage increases, the dominant factor for dam stability shifts from overflow to seepage. Differences in downstream slope failure degree caused by varying seepage resulted in three failure modes: overtopping failure, overtopping + seepage failure, and seepage failure. (2) In dams supported by coarser particles, seepage led to two stable modes: seepage stable and coarsening stable. The loss of finer particles within the dam further accelerates seepage development and reduces the rate of water level rise. (3) In dams supported by finer particles, seepage development accelerated the failure process. Under strong seepage conditions, compared to weaker conditions, burst time was shorter and peak discharge higher. (4) A prediction model for failure modes was established and validated using data from past studies. These results highlight that seepage does not always act as a destabilizing factor; instead, its role may shift from promoting failure to contributing to stability depending on the coupled effects of inflow, dam geometry, grain composition, and seepage intensity. This study provides a basis for understanding and predicting the failure mode transition of landslide dams under multi-factor coupled seepage conditions.</p>