The CVD diamond film possesses high hardness, excellent wear resistance, and it is fragile or peeling off and difficult to polish. As a new technique, polishing CVD diamond films by EDM method has been advanced in this paper. The surface of the diamond film must be coated with a layer of metal to make it conductive. Then EDM method is adopted to remove the peaks on the surface of the diamond films rapidly by discharge and erosion, which results in the high efficient polishing.First, metal coating on the surface of diamond film has been studied. Deposited experiments have been done by multi-arc ion plating and electroless deposition. The results show that electroless deposition is a perfect alternate to coat of compact and even layer, without macro metal globule, by easely coat and low cost.The discharge experiments of single pulse have been designed to study the effect of coating materials on polishing. The results show that Ni-P is in favour of evaporation of diamond film with good thermal conductivity, low melting and boiling point and catalysis of graphitization.Removal mechanism of CVD diamond polishing by EDM is advanced also. The studies show that the removal of diamond films is the result from compound effects, including vaporization of diamond, oxidation of diamond, graphitization of diamond, throwing action caused by explosion, micro-cleavages and stress concentration resulted from the heat effect of discharge.In this paper, the effects of EDM parameters (discharge energy, pulse frequency, pulse interval width and so on) on the efficiency and results of polishing CVD diamond films by EDM method are discussed. The effect of discharge energy is more remarkable than pulse width, electrode shape and thickness of coated layer.