While great interest has been focused on low-temperature plasma chemical vapor deposition, the pulsed high-temperature and high-density plasma beam was utilized to enhance diamond nucleation on Si substrate without damaging the smoothness of Si surface, and a nucleation density up to 10(9) cm(-2) was obtained. Scanning electron microscopy, atomic force microscopy, x-ray photoelectron spectroscopy, and transmission electron microscopy results indicated that after pretreated by this high power CH4 plasma,an amorphous modified layer rich in sp(3)-hybridized carbon was formed on the Si surface. This layer was believed to provide large amounts of nucleation sites for diamond.