<p>Strong earthquakes or heavy rainfall may trigger landslides, generating surge waves that pose serious threats to dam safety. This study develops and validates a coupled SPH-FEM framework to simulate multi-hazard interactions involving landslide-generated surges, reservoir dynamics, and their subsequent impact on dam structures. The methodology includes two key stages. First, a unified GPU-accelerated SPH framework simulates the landslide-induced surge dynamics and bidirectional fluid-structure interactions, with both fluid dynamics and auxiliary structural responses described using SPH particles. Second, spatiotemporally varying surge pressure fields, derived from the unified SPH framework, are mapped onto the high-resolution FEM substructure model for high-fidelity structural analysis. This hybrid approach effectively balances computational efficiency and physical fidelity, enabling comprehensive safety assessments of concrete dams subjected to landslide-induced surges. Parametric analyses reveal that surge dynamics and hydrodynamic pressure on the dam surface are predominantly governed by landslide characteristics, including volume, fragmentation degree, and proximity to the dam. Among these factors, the landslide fragmentation degree exhibits a non-monotonic influence. Moderate fragmentation leads to amplified secondary and tertiary wave amplitudes due to dynamic arrangement and reduced energy dissipation of the landslide mass. This finding underscores the significance of incorporating landslide fragmentation effects and site-specific topography into hazard assessments.</p>