The effect of fluid filling on the dynamic response of corrugated sandwich beams under simulated blast loading with close-celled metallic foam projectile was systematically investigated. Deformation and failure modes as well as displacement/contact force/energy absorption histories of water-filled sandwich beams were obtained at different impact levels and compared with those of empty sandwich beams. Subsequently, a combined smoothed particle hydrodynamics-finite element (SPH-FE) model was employed to simulate the dynamic responses of water-filled sandwich beams, explore the underlying mechanisms, and assess the influence of fluid-filling and sealing material on permanent beam deflection. Good agreement was achieved between numerical simulations and experimental measurements. Under impact loading, the filled liquid provides strong interaction between fluid and sandwich components owing to its inertia and incompressibility. Fluid-filling led to not only significantly reduced permanent deflection of both face sheets but also considerably enhanced resistance of the corrugated core against plastic buckling and progressive folding