The microscopic structures of the diamond films generated on Si (100) substrates by chemical vapor deposition have been studied by x-ray wide angle diffraction spectroscopy, grazing incidence x-ray scattering spectra, positrons annihilation lifetime spectroscopy, and qualitative software and Positronfit program. The di ffraction x-ray spectra show a structure difference between the near substrate p art (NSP) and near free-surface part (NFP) of the diamond film specimens, which reflect the weak ［111］texture in NSP and the strong［220］ texture in NFP. The positron annihilation lifetime spectroscopy of the specirnens and the analyzing data indicate that the majority of positrons annihilate around 200 ps and 400 p s. The vacancies, vacancy clusters, and voids were found in the film specimens, depending on the processes in which the chemical vapor deposition is generated.