Abstract: Ultrananocrystalline diamond film was deposited in CH₄and Ar gasm ixture with different concentrations of H₂by microwave plasma chem ical vapor deposition（MPCVD）.Scanning electronmicroscopy，Raman spectroscopy and X-ray diffraction w ere applied to characterize the film’s surfacemorphology and structure.The results showed that with the decreasing of hydrogen concentration，its averagegrains size and diamond phase is decreased，while the diamond film gradually tend to（111）faces grow th.And 1 190 cm^-1Raman peak were also found which had never previously appeared in the preparation of the diamond film.The film’swear resistancewas investigated by reciprocating type friction and wear tester.The research show thatw ith the decreasing of hydrogen concentration，ultrananocrystalline diamond’s hardness and elasticmoduluswas decreased，but the film’swear ratewas increased，and the change of friction coefficient wasnot relatively obvious.