Aluminum foam is a new type of material for shield of spacecrafts which bears fine characteristics when subjected to hypervelocity impact of space debris. A microstructure model of geometry for metallic foams was set up based on their manufacturing process and hypervelocity impact numerical simulations were conducted by self-programmed Smooth Particle Hydrodynamics. Six types of Al-foam stuffed shields were calculated and their ballistic limits were compared with each other. The results indicated that shield performance of Al-foam stuffed shield was better than that of solid Al-plate stuffed shield with the same areal density if the Al-foam was stuffed at appropriate position. The analyses of characteristic parameters of debris cloud of different shields indicated that Al-foam had better shield performance on small-size debris. The microstructure of Al-foam could effectively spread the perpendicular momentum of debris cloud and significantly increase the proportion of material liquefaction and gasification in debris cloud through multi-shock.