Cathode samples of nano-diamond by graphitization pretreatment with different temperatures were fabricated by electrophoresis, then the structures and morphologies of the cathode samples were characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD), and the field emission tests were conducted. The effects of graphitization pretreatment on the field emission characteristics of nano-diamond cathode surface on titanium substrate are studied. The results indicate that the surface morphologies of nano-diamond cathode samples after graphitization pretreatment change a lot, and the field emission characteristics in low-voltage area are improved obviously. However, in high-voltage area, the curve distortion happens, and it doesn’t conform the mechanism of field emission characteristics.