The transient diffusion processes in low-temperature epitaxial growth of Cu thin film on Cu（100） have been studied and classified by using molecular dynamics simulations with a hydrid tight-binding-like potential. The statistics indicate that the noticeable contribution to the surface mobility of adatoms comes from the impact cascade diffusion mechanism. Meanwhile

the observed oscillations of diffraction intensity show that a quasi layer-by-layer growth may take place at the temperature as low as 100K in the initial stage of thin-film formation.