Diamond film was grown by hot-filament chemical vapor deposition method. Carbon-halogen bond is much weaker than carbon-hydrogen bond. Therefore, carbon-halogen bond breaks easily at hot filament, and the halogen atoms produced will further induce reactions to generate hydrogen atoms to facilitate diamond film growth. The growth of high quality diamond film by CCl4/H2 mixture was succeeded. Faster nucleation rates of diamond film were observed by CH2C12 than those by CH4. The reaction mechanism will be discussed by camparing the results between CH4, CH2Cl2, CHCl3 and CCl4. They suggest that the active precursors for diamond growth are probably methyl radicals.