This paper present the investigation on collision cascades induced by gold clusters at 1keV/atom and aluminum clusters at 0.2keV/atom impacting on gold thin films. The energy spectra of projectiles at different time are calculated by molecular dynamics simulations. It is shown that the cluster atoms may even be accelerated during the slowing down process. The maximum energy of cluster atoms is found to be higher than their initial energy. In order to understand the acceleration mechanism, multiple collision processes have been studied. The possible energy gains of a cluster atom after double scatterings are calculated by the classical conservation laws.