By coating a platinum layer of about 40 nm thickness to a copper substrate seeded with ultradispersed nanodiamond particles (UDDs), faceted diamond with high density was detected. It presents a novel nucleation mechanism – carbon in UDDs was dissolved in platinum and was transferred through the platinum interlayer, followed the formation of sp3-bonded diamond clusters at the platinum surface, which was distinguished from UDDs without platinum modification layer. The diamond film was characterized by scanning electron microscope (SEM) with energy-dispersive X-rays, and laser Raman spectroscopy, respectively. After 4 h diamond growth, diamond film developed into two different layers: one nanocrystalline and one microcrystalline. Such a composite structure was attributed to the platinum layer that modified the interface properties of diamond nuclei and copper substrate at high temperature.