Nitrogen-incorporated distorted nanocrystalline diamond films were grown by microwave plasma enhanced chemical vapor deposition using N-2 and CH4 as precursors. Scanning electron microscopy, transmission electron microscopy, x-ray diffraction and Raman spectroscopy were used to characterize the films, which are composed of nanosized crystals with a local distorted but long-range ordered structure. A field electron emission threshold as low as 1.3 V/mu m has been obtained, and it decreases with a reduction of the methane to nitrogen ratio. The observed low emission threshold, good long-term stability and high maximum emission current (1 mA) suggest a new candidate for cold cathodes. In addition, an interesting switching phenomenon was found in the present films.