Abstract: The aluminum and carbon clusters impacting on gold thin films have been studied by molecular dynamics(MD) simulation. The initial energies are 0.1~0.2keV per atom. The energy spectra of target recoil atoms have been calculated as a function of time. It was shown that the target atoms may achieve more than twice of the maximum recoil energy in a single elastic collision. The effect has been traced to multiple hits by cluster atoms and the collisions between moving atoms.