Numerical simulating methodology is developed to predict the ballistic limit and impact force in order to investigate the critical failure of aluminum foam under the penetrating by blunt-nosed projectile. Mat26 in LS-DYNA was selected as the constitutive model for aluminum foam modeling on the basis of mechanical tests. Moreover, two control algorithms being executed in LS-DYNA helped in preventing the negative volume error. For the implementing aluminum foam, the ballistic limit velocity was obtained as 59.7 m/s. The research results show that impact force of blunt-nosed projectile acted with the maximum magnitude in the initial stage, but uniformly decreased at the plugging stage. The failure of aluminum foam majored with a compress-shear pattern when the penetration commenced. Until the plugging foam was compacted in some extent, tension crack may arise as the main failing. This work could help to optimize the experiment design and theoretical analysis.