Abstract: The effects of substrate pretreatment and processing parameters on the quality of diamond coating on WC-Co tools were reported. The diamond coatings were analyzed with scanning electron microscopy (SEM), X-ray diffraction (XRD) and laser Raman spectrometer (Raman). Efforts to improve the nucleation density and deposition speed were also undertaken. The results show that suitable substrate pretreatment can effectively control the overflow of cobalt and improve the quality of coating.