The compressive behaviors of aluminum foam under impact loading are investigated using FEM simulations. The plastic deformation takes place locally and an enhancement of force occurs at the impact end of the samples. By further investigation, this shock enhancement is found decreasing with relative density, but increasing with impact velocity. We also estimate the shock wave velocity. It is found that shock wave velocity increases significantly with impact velocity, but changes slightly with relative density. It is noted that the influence of the sample length on both the shock enhancement and the shock wave velocity is negligible. Finally, the relations of shock enhancement and shock wave velocity with impact velocity are obtained.