The initial growth of diamond coated on Cu-diamond inlay structure interlayer deposited by composite electroplating was investigated using a hot filament chemical vapor deposition method. The results show that with the increase of the growth time, the growth rate of diamond particles decreases and the irregular diamond particles protruding out of the Cu-diamond composite interlayer change into facet particles gradually. Second diamond grains preferentially nucleate at dihedral angle formed by homoepitaxial growth diamond particles and electroplating copper and the new dihedral angle between second crystal and copper promotes new second nuclei. This type of multiplying of second nucleation growth finally fills in the gaps of the large homoepitaxial diamond particles and forms continuously diamond film.