Abstract: The bonding conditon achieved by hot-pressing iron-based, nickel-based, copper-based and cobalt-based powders with TiN-coated diamonds has been studied by means of Transverse Rupture Strength(TRS) testing, SEM and EDAX. It is shown that the TRS is reduced by coating diamond with TiN in iron-based, nickel-based and copper-based competes. In iron or nickel based composites, the fracture mostly occurred on the TiN-matrix interface, and the main elements (Fe,Ni etc.) has diffused to diamond surface and caused small pert of the coating scale off the diamond. In copper- based and cobalt-based composites, the fracture mostly occurred in the matrix,and TiN coatings has been kept intact and the TiN surface was evenly coated by cobalt-matrix in the fracture surface.TiN has a very small solubility and its velocity of diffusion is the cobalt-based matrix.