Although various diamond polishing techniques have been studied for many years, no individual method can polish free-standing CVD diamond film with high efficiency and high polishing quality. This paper investigates polishing CVD diamond film by the combination of electro-discharge machining (EDM) and chemical mechanical polishing (CMP). Scanning electro microscopy, Optical microscopy, Energy dispersive X-ray analysis, Talysurf surface profiler and Raman spectroscopy were used to evaluate the surface integrity and quality of diamond film before and after polishing. Based on the experimental results, the material removal during EDM process can be a chemo-mechanical process, including gasification, melting, sputtering, oxidation and graphitization. While in CMP process, diamond was removed under the mechanical and tribochemical interaction. The combination of EDM and CMP has advantages of high efficiency, high polishing quality and low damage. It is suitable to polish large area free-standing CVD diamond film.