Abstract: A rigid-plastic analytical model is developed for the dynamic response of a sandwich beam with lattice truss cores. The beam is simply supported at the ends without axial rest raints，and the impulsive loads are uniformly distributed over the span. The maximum deflection and structural response time of the sandwich beam predicted by the rigid-plastic theory and three-dimensional FEM are compared. It is found that the theoretical predictions of the maximum deflection and structural response time are in good agreement with those of FEM，and sandwich beams with lattice truss cores can offer superior shock resistance to impulsive loadings in comparison with monolithic beams of the same mass and material. Through an optimal design for the pyramidal cores，it is revealed that the dynamic response of the simply supported sandwich beam without axial rest raints is sensitive to the relative density and thickness of the lattices truss core，and the angle of inclination between truss and face sheet. As the applied impulse per unit area is enhanced，the maximum deflection of the sandwich beam increases. Refined finite element modeling of the pyramidal truss core sandwich beam made from strain-rate sensitive 304 stainless steel is employed. The finite element calculations reveal that the maximum deflection of the sandwich beam is decreased as the strain-rate effect is considered.