<p>The inverse graining deposit (IGD) resulting from landslides is frequently susceptible to seepage-induced erosion failure, posing a significant threat to infrastructure, exemplified by the Sichuan-Tibet Railway, as well as the local population. In this study, the phenomenon of fluid flow-induced particle migration within IGD has been examined through seepage tests utilizing a proprietary experimental apparatus and numerical simulations utilizing a coupled computational fluid dynamics-discrete element method (CFD-DEM) coupling scheme, focusing on elucidating particle dynamics and the underlying migration mechanisms. The experimental findings reveal that continuously graded IGD and discontinuously graded IGD are vulnerable to localized erosion and piping erosion, respectively. Furthermore, the critical hydraulic gradient for erosion diminishes with the reduction in fine particle content, unevenness coefficient, and hydraulic gradient in the lower layer. Numerical simulations are conducted to analyze the erosion mechanism and to assess the impact of fine particle migration and particle content on the overall stability. The findings from these simulations indicate that the absence of fine particles in the middle and upper layers of IGD leads to an inability to replenish particle loss in the lower layer, thereby exacerbating erosion. Consequently, IGD, particularly with those with discontinuous gradation, may play a pivotal role in promoting erosion behavior. It is imperative to conduct further research to examine the influence of layer number, gradation continuity, and the order of particle size distribution in situ, to assess the stability of the deposit under seepage conditions.</p>