Abstract: The nucleation and growth of diamond was investigated by changing methane concentration during diamond deposition using the self-made hot-filament CVD apparatus. The results show that after nucleation, new nucleus can form again on the silicon substrate surface when the methane concentration increases. However, the final nucleus density obtained on gradually increasing the methane concentration from 0.6% to 1.2% is smaller than that deposited at a methane concentration of 1.2%. The growth rate of the new nuclei is larger than that of the earlier and thus all nuclei tend to have the same size.