Electron field emission property of boron doping nano-crystalline diamond was discussed. Various techniques were applied to enhance the nucleation rate for growing diamond films. NCD films of various nucleation conditions were prepared from methane-hydrogen mixture by microwave plasma enhanced chemical vapor deposition (PECVD) technique. The morphologies and bonding structures of these films were characterized by field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), Raman spectroscopy and X-ray diffraction (XRD). The main factor modifying the electron field emission properties is assumed to be the increase in proportion of sp2-bonded grain boundaries in finer grain nano-diamond films.