Molecular dynamics (MD) simulation was used to study the growth process of dia mond_like carbon (DLC) films synthesized via ion_beam_assisted deposition (IBAD ). The C2 molecules and Ar ions were selected as deposition and assis tance pr ojectiles, respectively. The influence of the impact energy of Ar as well as the assistance/deposition atomic ratio (Ar/C), on the film structure was investiga ted. The transient mobility and the migration of C adatoms caused by Ar impact were studied. Our results indicate that the impact-induced high recoil energy a nd displacement of deposited C atoms play a leading role in the growth of DLC f ilms. This can be attributed to the incident energy and momentum of assistance Ar. Our results agree well with the experimental observation. Furthermore, it e xplains the growth mechanism partly.