Since the field emission properties were reported in 1995, the carbon nanotubes have been regarded as the most promising material for the cathode. The field emission properties of the carbon nanotubes are measured under different conditions in order to improve the field emission abilities of carbon nanotube. The effects of thermal accumulation of the anode on the field emission properties are studied. The results show that higher-current and higher-current density could be acquired by suppressing the thermal accumulation.