Abstract: CVD diamond coating on WC-6%Co for cutting tools has been investigated. The substrates were etched by HCl:HNO₃:H₃O(volume fraction) 1:1:1 solution at 80℃ for 15min to remove the cobalt from the surface. In order to enhance diamond nucleation, ultrasonic scratching pretreatment was applied by using diamond powder with 40μm parti-cle and the mixture of diamond powder with 1.5μm particle and TaC powder with 20 μm particle. The diamond deposition was performed by the hot filament CVD method.Adhesion was checked using Rockwell hardness machine with a loading capacity of 1 500 N, the experimental results show that the adhesion of CVD diamond coating to WC-6%Co substrate by ultrasonic scratched with diamond powder of 40 μ m particle is better than that of the mixture of diamond powder with 1.5μm particle and TaC powder with 20μm particle.