Nanocrystalline diamond compact possesses not only the advantageous performance of polycrystalline diamond but also the high strength and the high toughness of nano-ceramics. However, single-phase nanocrystalline diamond compact is very difficult to sinter because of a huge amount of oxygen-containing and nitrogen-containing functional groups absorbed on the surface of nanocrystalline diamond. In this paper, atomic layer deposition (ALD) method has been used to coat nanocrystalline diamond with titanium, which will promote the bonding of nanocrystalline diamond as the bond in polycrystalline diamond. In vacuum, the H2 and TiCl4 reactants were employed alternately in an ABAB… binary reaction sequence to achieve Ti layer, which reacted with diamond matrix and formed TiC in the coating, realizing strong chemical bonding between the coating and the diamond. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were utilized to study the structure and the morphology of the coating. The results confirmed the formation of titanium carbide at the depositing temperature 500°C. The darker spots and strips observed on nanocrystalline diamond particles by TEM were proved to be TiC and the nucleation and subsequent growth of TiC preferentially occurred in the defects as twin zones and dislocation areas on diamond surfaces.