films with different qualities and orientation were grown by the hot-filament CVD technique. The dielectric properties of these films before and after annealing were investigated in detail. A study of the relationship between the different deposition conditions and annealing process with respect to the dielectric properties was carried out. These CVD diamond films were also characterized with Raman spectroscopy, XRD and I2V characteristics. High-quality CVD diamond films were grown on Si substrate mechanically scratched with diamond powder. The annealing process reduces the hydrogen contamination of the films and therefore improves the film quality. CVD diamond films with good electric properties such as a resistivity of 1.2×1011Ωcm at a voltage of 50V, a dielectric constant of 5.73 and a dielectric loss of 0.02 at a frequency of 2MHz were obtained.