Abstract: With the vacuum hot pressing diffusion method, Ti coating layer was prepared on the surface of polycrystalline diamond to investigate the formation mechanism of the interface during diamond metallization. The surface morphology, interface structure and phase composition of the Ti coating layer were analyzed with a scanning electron microscope and an X-ray diffractometer. The interfacial elements were analyzed with an energy disperse spectrometer. The width of the element diffusion zone between polycrystalline diamond and Ti layer and the free enthalpy change for the chemical reaction to generate TiC were calculated. The research results show that flat and dense Ti layer is formed on the surface of polycrystalline diamond. There is diffusion of carbon, Ti and cobalt elements on bonding interface between Ti coating layer and polycrystalline diamond. An element diffusion zone with a certain width is generated on bonding interface. At the same time, spot-shaped TiC particles are formed on diamond surface. The vacuum hot pressing diffusion method can realize a chemical combination between diamond grain and a Ti layer, and can improve the bonding strength between diamond grain and Ti layer.