Abstract: The a-C:H (hydrogenated diamond like carbon) films were deposited on stainless steel substrates by means of radio frequency plasma enhanced chemical vapor deposition process and the Raman spectrum was applied to the characterization of the microstructure of the films. Especially, the Lorentzian decomposition was carried out for the Raman spectra to estimate the sp³ content in the films deposited so as to investigate the effects of the voltage during deposition process and transition layer on the growth of film and sp³ content in the resultant film. The results indicated that Lorentzian decomposition for the Raman spectra can effectively characterize the microstructure of a-C:H film, and in the deposition process the voltage and transition layer affect greatly the growth of a-C:H film. Under conditions that the characterization was done, the sp³ content in a-C:H film deposited under 2500 V with Ti/TiN/TiC as transition layer comes up to its maximum value.