Boron-doped diamond (BDD) is an electrode material applied in advanced oxidation technology for wastewater treatment, the choice of its substrate material is one of the key considerations for making electrode coating. The appropriate substrate material enhances the adhesion of the film to the substrate and then lengthens the service life of the electrode. In this work, cemented carbide (WC-Co) which has a low coefficient of thermal expansion is employed as the substrate, and microcrystalline and nanocrystalline BDD films are prepared by hot filament chemical vapor deposition (HFCVD). The two types of WC-Co/BDD electrodes were investigated by field emission scanning electron microscopy (FE-SEM), micro-Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and cyclic voltammetric. During the fixed deposition time, the growth rate of microcrystalline films is 1.5 times that of nanocrystalline films, and the residual stress of microcrystalline films (1.7 GPa) is greater than that of nanocrystalline films (-0.6 GPa). The two varieties of WC-Co/BDD electrodes exhibit a wide potential window greater than 3.7 V and featureless background current in 0.5 mol/L H2SO4 solution; they have a quasi-reversible behavior in the K3［Fe(CN)6］ redox system, which are similar to conventional Si, Nb, Ti based BDD electrodes. Subsequently, the electrodes were characterized by replicated experiments for oxidating phenol and an accelerated life test (ALT). The results show that the lifetime of the nano-electrode (about 423 h) is clearly superior to that of the micro-electrode (about 310 h) when identical conditions are used in the ALT. In the phenol oxidation experiments, both electrodes show a good mineralization impact on phenol; the current efficiency of the micro-electrode and nano-electrode are 88%~94%, which is close to standard BDD electrode. As a result, WC-Co might be an appropriate substrate for the BDD electrodes in wastewater treatment applications.