Abstract: Oriented carbon nanotubes film was synthesized on Si substrates by radio-frequency plasma enhanced chemical vapor deposition via decomposing acetylene at low temperature with Ni as catalyst.The distribution of Ni particles and morphology of carbon nanotubes film were characterized by using scanning electron microscope.The effect of auxiliary gases on catalyst pretreatment and growth process of carbon nanotubes were discussed.The results showed that the grain size and distribution density of catalyst particles etched by different flow ratio of gases(hydrogen and nitrogen) had strong effect on the morphology of carbon nanotubes.A proper flow ratio of hydrogen and nitrogen tended to produce the defect-free carbon nanotubes and to improve the growth of oriented films.When the ratio of hydrogen and nitrogen was 20:5,the size of Ni particles was small,the density high and the size distribution range narrow.Furthermore,when the ratio was 20:15,the carbon nanotubes film with high purity can be obtained.