CNx films were prepared by using microwave plasma-enhanced chemical vapor phase deposition. As-deposited films were analyzed by x-ray photoelectron spectroscopy, x-ray diffraction, scanning electron microscopy and Raman spectroscopy. Field electron emission characteristics of thin films were studied. Experimental results indicate that the film structure and properties of the field electron emission are related to flow ratio of N2 to H2 while the flow rate of CH4 was kept at 8 sccm. When the flow ratio of N2 to H2 was 50/50 sccm, the obtained film had a nano-crystalline graphitic structure with curved basal planes (fullerene-like structure) and excellent properties of field electron emission. The turn-on field decreased to 1.1 V/μm. At an electric field of 5.9V/μm, the average current density was 70μA/cm2 and emission sites density was larger than 1×104cm-2.