The nucleation behavior of nanodiamond films and the associated electron field emission properties were investigated. Among the important CVD parameters, the methane/hydrogen ratio and the total pressure impose most markedly effect, whereas the microwave power and the boron content show least significant effect on the nucleation behavior for the nanodiamonds. Presumably, the prime factor modifying the rate of formation of diamond nuclei is the proportion of C+- and H+-species contained in the plasma. The bias voltage applied for nucleation of diamonds show more marked effect on improving the electron field emission capacity for the nanodiamonds than the boron-content does. It is ascribed to the increase in proportion of grain boundaries, as the grain boundaries are highly conductive and are good emission sites.