Abstract: The catastrophic process of rainfall-induced landslides is governed by the multiphysics coupling of structural, stress, seepage, and deformation fields, exhibiting high complexity in its underlying mechanisms. In this paper, the failure mechanism of a slope containing an interlayer and a fracture under rainfall conditions is investigated through integrated physical flume tests and discrete element method(DEM)simulations. Experimental results demonstrate that the presence of the fracture and interlayer significantly alters the seepage paths, forming preferential flow channels that facilitate rapid rainwater infiltration. This process leads to localized pore-water pressure buildup and a consequent reduction in soil strength, ultimately triggering slope failure. Based on these observations, a coupled DEM model is developed that incorporates moisture transport and dynamic strength reduction. In the model, each particle is assigned a moisture content attribute, and rainfall infiltration is simulated by maintaining surface particles in a saturated state. This approach enables accurate reproduction of the coupled hydro-mechanical-deformation process during rainfall. The numerical results agree well with the experimental data, successfully capturing key features such as preferential moisture migration and the hysteresis of pore pressure response. This study validates the multi-field interaction mechanisms in heterogeneous slopes and provides deeper insight into the failure processes of rainfall-induced landslides under coupled seepage-stress-deformation conditions.