Hydrogenated amorphous carbon films were fabricated by using layer-by-layer deposition method and hydrogen dilution method in a small d.c.-assisted plasma enhanced chemical vapor deposition system. It was found that the hydrogen plasma treatment could change the sp2/sp3 ratio to some extent by chemical etching. The improvements of field emission characteristics were observed compared with that from conventionally deposited a-C films, which can be attributed to the large field enhancement effect due to the inhomogeneous distribution of nanometer scale sp2 clusters and the reduction of the surface emission barrier due to the hydrogen termination. Hydrogenated amorphous carbon films were fabricated by using layer-by-layer deposition method and hydrogen dilution method in a small dc-assisted plasma enhanced chemical vapor deposition system. It was found that the hydrogen plasma treatment could change the sp2 / sp3 ratio to some extent by chemical etching. The improvements of field emission characteristics were observed compared with that from conventionally deposited aC films, which can be attributed to the large field enhancement effect due to the inhomogeneous distribution of nanometer scale sp2 clusters and the reduction of the surface emission barrier due to the hydrogen termination.