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.