Two kinds of micron diamond grain thin film were obtained by microwave plasma chemical vapor deposition method under different conditions. The composition of the two kinds of thin film were analyzed by Raman spectroscopy and Xray apparatus, and the surface morphology was analyzed by scanning electron microscope (SEM), and the field emission performance was studied by the field emission device with secondary structure. Finally, the characteristics of micron diamond films with excellent field emission properties were analyzed and discussed.