It is well known that amorphous carbon and related films consist of nano-sized carbon clusters. With the incorporation of hydrogen into these films, the hydrogen termination limits the cluster size and decreases the bond strength among clusters. In this study, dehydrogenation from amorphous hydrogenated carbon nitride films was accomplished using 3.75 MeV-He2+ irradiation. The hydrogen atoms forming methyl and ethylene groups were mainly removed from the film during the irradiation procedure. With the progress of dehydrogenation from methyl and ethylene groups, the degree of order of the atomic configuration became large, resulting in an increase of the cluster size. The mechanical properties of amorphous films were improved due to cluster growth.