Nano-sheet carbon films are prepared on Si wafers by means of quartz-tube microwave plasma chemical vapour deposition (MPCVD) in a gas mixture of hydrogen and methane. The structure of the fabricated films is investigated by using field emission scanning electron microscope (FESEM) and Raman spectroscopy. These nano-carbon films are possessed of good field emission (FE) characteristics with a low threshold field of 2.6 V/ìm and a high current density of 12.6 mA/cm2 at an electric field of 9 V/ìm. As the FE currents tend to be saturated in a high E region, no simple Fowler-Nordheim (F-N) model is applicable. A modified F-N model considering statistic effects of FE tip structures and a space-charge-limited-current (SCLC) effect is applied successfully to explaining the FE data observed at low and high electric fields, respectively.