Carbon,CNx and BCN nanotubes were synthesized by pyrolysis at 860℃ and purified. Thin films of the purified samples were fabricated by a screen-printing method. The field emission effect of these films was compared. It was found that the turn-on field was 2.22，1.1 and 4.4V/μm,and the current density at 5.7V/μm was 1400，3000 and ＜50μA/cm2 for C, CNx and BCN nanotubes,respectively. The electron field emission property of the CNx nanotubes was better than the carbon nanotubes while that of BCN nanotubes was the worst. The origin of the differences in field emission of these films was explained.