Abstract: Cellular projectiles are widely used in the impact tests of protective structures, but the actual loads of cellular projectiles acting on the tested sandwich structures are still unclear. In this paper, the dynamic response process of a uniform/graded cellular projectile impacting a foam sandwich beam is studied through theoretical analysis, numerical simulation, and impact tests. The foam sandwich beam is equivalent to a monolithic beam to simplify the analysis. Based on the shock wave model of the cellular projectile and the equivalent response model of the foam sandwich beam, a coupling analysis model of the cellular projectile impacting the foam sandwich beam is developed, and its governing equations are presented. Meso-finite element simulations of a uniform/graded cellular projectile impacting a foam sandwich beam are carried out, and impact tests are performed on the test platform of cellular projectiles. It is found that the coupling analysis model can accurately predict the process of a cellular projectile impacting a foam sandwich beam and the impact pressure of the cellular projectile. Subjected by cellular projectiles with the same initial momentum but different density distribution or initial velocity, foam sandwich beams with the same configuration present different mechanical response processes, which demonstrates that the impact of cellular projectiles cannot be simply equivalent to impulse loading, and the coupling effect between the projectile and the sandwich beam cannot be ignored. Compared with uniform cellular projectiles, the impact pressure waveform of the graded cellular projectile is sharper and shows stronger nonlinearity during its attenuation. This study clarifies the loading effect of cellular projectiles on foam sandwich beams and lays a theoretical foundation for the optimal design of cellular projectiles simulating blast loads.