The structural stability and the electronic field emission properties of cone-capped carbon nanotubes have been deeply analyzed by the density functional theory. The results show that their structurs are much more stable than those of carbon nanocones and carbon nanotubes sealed with a C30 hemisphere, and their electronic field emission properties are closely related to the configuration of cone apex and the magnitude of cone angle. Meanwhile, the combination property of cone1@(6,6) with a ridge-shaped tip and 38.9° cone angle is optimal. When it is used as a field emission source the field emission current density and the lifetime of device will be remarkably increased.