In this paper, the growth process of diamond polycrystalline carbon films and the emission properties of carbon films at different growth stage were studied. A series of carbon films were prepared by depositing the substrate in a microwave plasma chemical vapor deposition chamber after coating the ceramic substrate with a layer of metal titanium. The morphology and composition of carbon films were analyzed by scanning electron microscopy (SEM), Raman spectroscopy (Raman) and X-ray diffraction (XRD). Finally, the field emission performance of carbon film was tested by using the secondary structure field launcher. The change regularity of diamond polycrystalline carbon film is discussed, and the excellent field emission mechanism of diamond polycrystalline carbon film is studied.