The diamond film was prepared on Si(111) by the plasma assistant hot-filament chemical vapor deposition. Before the experiment, the thin sand paper was first employed to nick the wafer for 5 minutes. The diamond abrasive abraded the wafer for 15 minutes. Then the wafer was cleaned in the deionized water by the ultrasonic and was dried by the blower. The influences of the nucleation and growth of diamond film were studied on the following conditions: CH_4/H_2=1%~5%.substrate temperature form 700℃ -880 ℃. bias-voltage form 0V-400V, pressure form 1kpa~5kpa. The samples were characterized by SEM and XRD. We obtained the following results: ①The pretreated of the substrate played an important role on the diamond nucleation. The nucleation density could be promoted after pretreated.② The nucleation density and deposition rate were increased with increase the content of methane, however the quality of diamond film became bad.③The temperature of the substrate was vital for the diamond deposition. The deposition rate was increased and the noncrystal carbon was decreased with increase the substrate temperature. The substrate temperature not only influenced the deposition rate, but also influenced the surface microstructure of diamond film.④Bias-voltage can obviously improve the nucleation density and improve the quality of diamond film. The nucleation density can reach 10~(11) cm~(-2).We also prepared diamond/TiC composite film.