Molecular dynamics (MD) simulation is made to study growth of diamond-like carbon (DLC) films via ion-beam-assisted deposition (IBAD).C₂ molecules and H ions are selected as deposition projectiles and Ar ions are selected as assistance projectiles.At fixed incident energy and varied ration (Ar/C),assisted deposition of film is investigated.Transient mobility and migration of C atoms due to Ar impact is investigated.It shows that the impact-induced high recoil energy and displacement of deposited C atoms play a key role in growth of DLC films.It is attributed to incident energy and momentum of assistance Ar.The results agree well with experimental observation.It helps understanding of the growth mechanism.