With use of electron-assisted chemical vapour deposition (EACVD) technology, nanocrystalline diamond films are successfully deposited on an α-SiC single phase ceramics substrate by means of reduction of the reactive gas pressure. The structure and surface morphology of the deposited films are characterized by Raman spectroscopy, x-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and atomic force microscopy(AFM). The results examined by FE-SEM and AFM show that when the gas pressure was reduced to 0.5-1 kPa, the surface grain size and surface roughness of the diamond film are decreased greatly to 18-32nm and34-58nm respectively. The grain Sizes estimated from full with at half maximum of (111) XRD peak by the Scherrer formula are 6-28nm. However,. Too. High secondary nucleation rate may result in pores and defects in the deposited films. Only at suitable gas pressure (1 kPa) to deposit films can we obtain densification and better quality nanocrystalline films.