<p>Debris flows, as a type of high-speed, long-range geological hazard, exhibit movement characteristics and deposit distributions significantly influenced by particle gradation. However, the mechanisms through which gradation factors regulate energy transformation and dispersal capacity remain unclear. This study focuses on the geological background of debris flows initiated by the activation of rockfall deposits at Huashan, Jinan, which are triggered by typhoon-induced torrential rainfall. Using the PFC3D discrete-element numerical simulation method, we developed four gradation schemes: uniform, unimodal continuous, bimodal discontinuous, and wide-graded particle distributions. We quantitatively analyzed particle movement processes, energy evolution, and accumulation characteristics under varying gradation scenarios. The results indicate that gradation significantly influences energy release rhythm, with wide-graded and bimodal gradations causing more violent collisions due to marked particle size disparities. The energy peak for wide-graded gradation can reach up to 500&#xa0;kJ (comparable to the kinetic energy of a vehicle at 90&#xa0;km/h), which enhances movement instability. Furthermore, particle-terrain collisions dominate travel distance; the higher this collision proportion, the farther particles migrate. The study further found that, despite the significant effects of gradation on individual particle energy processes, The overall dispersal range is primarily constrained by the lateral topography of the valley channel, slope gradients, and channel morphology, exhibiting a typical “channel effect.” This research reveals, at the particle scale, the regulatory mechanisms by which gradation affects the dynamic behavior of debris flows, providing a theoretical basis and simulation support for risk assessment and mitigation planning of debris flow disasters in mountainous areas.</p>