Abstract: Three kinds of diamond polycrystalline carbon films were prepared under different conditions by placing ceramic substrates covered with titanium into a thin plasma cavity. The morphology and structure of carbon films were analysed by scanning electron microscopy, Raman spectroscopy and X-ray apparatus. The field emission properties of carbon films were studied by secondary structure, and the best emission properties were obtained. The causes of the three kinds of carbon films and the different field emission properties are analysed, which makes some contributions to the preparation of excellent field emission cathode materials.