Two kinds of Cu substrates were used to grow diamond films,one of them being 99.99% polycrystalline Cu foil and the other 99.95% phosphorus deoxidized Cu foil.Large-area,free-standing polycrystalline diamond films were obtained by hot filament CVD on both substrates.The diamond films on the two kinds of Cu substrates were comparatively investigated by high resolution optical microscopy,scanning electron microscopy,Raman spectroscopy,and X-ray diffraction.The quality of films on deoxidized Cu are not worse than that on polycrystalline Cu,while the nucleation densities ,growth rate and stress in film on deoxidized Cu is higher than those on polycrystalline Cu.It is indicated that the annealing process and optimized growth conditions must be used to obtain large-area continuous diamond films.