Hard hydrogenated amorphous carbon (so-called diamond-like carbon,DLC) films with superior mechanical properties,wear resistance and biocompatibility have been used on the surface modification of artificial joint.These properties were determined by the structure of films,such as the content of hydrogen,the proportion of sp3 and sp2 and the optical band gap.In order to research the effect of pulse bias voltage on the structure of the films,amorphous hydrogenated carbon films have been deposited on Si(100) substrate using electron cyclotron resonance plasma enhance chemical vapor deposition (ECR-PECVD) with mixtures of hydrogen and acetylene gas.During deposition,the microwave power was set to 400W,the pressure in vacuum chamber was set to 0.5Pa.The pulse bias voltage (20KHz,duty ratio 20%) was varied from-100V to -400V for the different sample deposition runs.The thickness and the residual stress were measured by surface profilometer.The optical band gap was measured by UV-VIS spectrometer.The bonding nature of the a-C:H films was characterized by visible Raman spectra,Fourier transform infrared (FTIR) spectroscopy.The results showed that the bias voltage strongly affected the structure of the films.The deposition rate decreased with the increasing of bias pulse voltage,But increasing of bias pulse voltage,the optical band gap Egincreased from 3.4 eV to 3.7eV and the residual stress of the a-C:H films increased to IGPa at-400V bias pulse.The FTIR spectra showed that the hydrogen content decreased with the increasing of bias pulse voltage and polymeric vibration model appeared in the film of-100V bias pulse.