In this investigation, conventional microcrystalline diamond (MCD) and boron doped diamond (BDD) films are deposited onto commercially available cemented tungsten carbide (WC-Co) Ball-nose endmills by using hot filament chemical vapour deposition (HFCVD). The quality and properties of the as-deposited diamond film are characterized by field emission scanning electron microscope (FESEM) and Raman spectroscopy. Milling tests of graphite materials using MCD, BDD coated and uncoated tool are carried out. Experiment results reveal that BDD films possess higher adhesive strength to the substrate than that of MCD films, and the BDD coated mills allow to be given smaller flank wear and longer tool life, when compared with MCD coated and uncoated WC-Co tools. Cutting performances of WC-Co mills in graphite milling are greatly improved by BDD coating, and typically more than 10 times the tool life is obtained. The research results are of great significance for high efficiency and quality machining of graphite materials.