<p>Hazard assessment of landslide-induced impulse wave in high-dam reservoirs requires explicit quantification of the cascading processes from slope instability to wave impact. Previous methods often decouple the failure probabilities of slopes from hydrodynamic consequences, hardly considering the nonlinear amplification of cascading hazards. In this study, a physically-based hazard assessment framework from probability to consequence is established for the reservoir landslide in the upstream of the dam. The failure probabilities and models of slope under different reservoir levels are quantified via a Monte Carlo–based limit equilibrium approach. The failure models of slope are then simulated by the multiphase smoothed particle hydrodynamics (SPH) model, for considering landslide impact, wave evolution, and dam interaction. Reservoir level has a dual effect on hazard assessment via the failure probability of the slope and wave impact intensity. The secondary and localized failure of slopes under normal water level produces amplified wave heights due to enhanced impulse transfer and reduced energy dissipation, resulting in comparatively higher integrated risk. In contrast, other failure modes exhibit lower wave amplification despite comparable instability probabilities. Overall, this study provides a quantitative and physically-based framework for assessing landslide-induced wave hazard in high-dam reservoirs, supporting risk-informed safety management and hazard mitigation.</p>