In order to study the reflection and sputtering by low-energy cluster impact, we have performed the molecular dynamics (MD) simulations of (Cu)55 cluster impact on a Pt (111) surface with an energy of 100 eV/atom, and compared with those of monatomic Cu ion bombardment with the same energy per atom. As to the reflection, the lower-part cluster atoms are more reflected than the upper-part cluster ... [Show full abstract] atoms at the very-early stage of cluster impact. This is the high-density effect on the reflection by cluster impact. However, the upper-part cluster atoms are more reflected than the lower-part cluster atoms after all. As to the sputtering, the sputtering yield for cluster impact is by far larger than that for monatomic ion bombardment. In the case of monatomic ion bombardment, Pt atoms tend to be sputtered in the close-packed directions of the Pt (111) target. In the case of cluster impact, Pt atoms are fairly sputtered in the normal and lateral directions as well as the close-packed directions. These results for sputtering agree with experimental observations and other simulation results. The sputtering in the normal and lateral directions is certainly enhanced due to cluster impact, but the high–density effect on the sputtering by cluster impact is not clearly observed. The high-density effect is not the main effect on the reflection and sputtering by cluster impact, and it does not seem to be observable experimentally.