Abstract: Currently, performance testing of flexible barrier only focus on rockfall impacts, lacking research on the coupled dynamic response under slope debris flow impact. In this study, based on LS-DYNA, a full-scale impact test with a nominal energy level of 5000 kJ of flexible barrier was firstly back-analyzed, comparing and analyzing the key rope forces, elongation of energy dissipators, and buffer distance to verify the effectiveness of the computational model. Next, an ALE-FEM numerical calculation model was built to investigate the mechanical response characteristics of the flexible barrier under slope debris flow impact, and compared them with rockfall impact conditions. Finally, parametric numerical simulations of debris flow velocity and impact energy were carried out to analyze the dissipation and transformation characteristics of impact energy and explore the ultimate protective capacity of flexible barrier from an energy perspective. The results showed that the flexible barrier can successfully intercept slope debris flows under the nominal energy levels, with overall mechanical responses significantly smaller than those under rockfall impacts. The impact energy mainly converted into internal energy of debris flows. Flexible barriers can successfully intercept slope debris flows up to four times the impact energy of rockfalls.