In this study, micron diamond polycrystalline films were prepared on the ceramic substrate coated with titanium by microwave plasma chemical vapor deposition method, with the mixed gases of methane and hydrogen as the reactive gases. The chemical composition, microstructure and surface morphology of the films were analyzed by SEM, Raman spectroscopy and X-ray experiments. The field emission performance of the thin films was studied by the field emission instrument of the secondary structure and scanning tunneling microscope, and the results indicated that the emission point of the micron diamond polycrystalline film mainly originated from the polycrystalline particles. The emission properties of different areas on the surface of single polycrystalline particles were further studied, and it is found that the field emission property will be affected by various factors.