Ultradispersed nanodiamond powder, which was synthesized by explosive detonation, was used as the coating material on the substrate for the purpose of enhancing nucleation density and promoting growth of diamond thin films. The experiment show that in comparison with the scratching pretreatment with diamond particles of approximately micrometers in diameter, the pretreatment with the nanodiamond powder can not only enhances nucleation density and film growth rate, but also improves the quality of the grown-up films significantly. The films by this pretreatment possess a lot of outstanding properties, such as compact structure, low surface roughness, fine facets and high crystalline quality. In contrast, the films on the scratched substrate exhibit significant second nucleation. As an important result, present experiment confirms that the pretreatment with the explosive detonation nanodiamond powder is very cost- effective economically; reproducible and non-damaging to the substrates of diamond film growth as well.