Abstract: High-altitude rockfalls typically exhibit significant falling heights and high potential energy, resulting in pronounced dynamic fragmentation effects during motion. As such, determining the disaster range of high-altitude rockfalls remains a key challenge in disaster prevention and mitigation research. This study systematically examines how the initial motion states of falling rocks influence migration distance and dynamic fragmentation after impacting the slope. The motion states are decomposed into translational and rotational forms. A series of discrete element method (DEM) simulations were conducted under varying initial motion states to analyze the resulting particle migration distances and fragmentation levels. The results show that initial motion states significantly affect the degree of rock fragmentation and consequently, the migration behavior of rockfall debris. Specifically, an increase in initial horizontal velocity is positively correlated with the maximum migration distance of fragments but negatively correlated with the centroid migration distance. In contract, higher initial angular velocity shows a negative correlated with both maximum and centroid migration distances. Variations in initial motion states primarily affect the distribution of medium- to large-sized fragments, while the differences in fine particle distributions are less pronounced. Furthurmore, increasing initial horizontal velocity promotes more severe rock fragmentation, resulting in a narrower particle size distribution and improving sorting. Conversely, greater initial angular velocity inhibits rock fragmentation, producing a broader particle size range and reduced sorting performance. These findings provide valuable insights for predicting the potential hazard zones of rockfalls and supporting the design of effective protective measures.