Abstract: In order to improve the adhesion of the diamond to the WC-6%Co insert substrate, boronizing approach from solid powder was adopted the first time to deal with the surface cobalt of the substrate. A layer of the CoB and CoB, intermetallic compounds chemically bonded to the substrate was yielded during boronizing at 1 000℃×4 h, and the layer can effectively prevent the diffusion of the cobalt up to the surface during diamond deposition; the layer can relieve residual styesses at the diamond-carbide interface too. The diamond coating on the substrate by boronizing pretreatment shows a further significant adhesion improvement.