In this paper, the mechanical behaviours of open-cell and closed-cell aluminium foams against spherical-nosed projectile penetration are studied theoretically. An analytical model based on dynamic cavity expansion theory and previous experiment data is presented. The analytical equations are derived for the penetration resistance and the final penetration depth during the whole penetrating process. The effects of the mass density of target material, the geometry and initial velocity of the projectiles on the final penetration depth are investigated in detail. It is shown that the final penetration depth mostly lie on the density of aluminium foams and the kinetic energy of projectile. When the density of target is smaller, the final penetration depth of projectile in the closed-cell aluminium foams target is obviously smaller than that in the open-cell aluminium foams target. Meanwhile, with the increase of density of target and the decrease of initial impact velocity, the difference of the capacity of absorbing energy between open-cell and closed-cell aluminium foams targets becomes gradually narrow.