A field emission device (6), in accordance with a preferred embodiment, includes a cathode electrode (61), a gate electrode (64), a separator (62), and a number of emissive units (63) composed of an emissive material. The separator includes an insulating portion (621) and a number of conductive portions (622). The insulating portion of the separator is configured between the cathode electrode and the gate electrode for insulating the cathode electrode from the gate electrode. The emissive units are configured on the separator at positions proximate to two sides of the gate electrode. The emissive units are in connection with the cathode electrode via the conductive portions respectively. The emissive units are distributed on the separator adjacent to two sides of the gate electrode, which promotes an ability of emitting electrons from the emissive material and the emitted electrons to be guided by the gate electrode toward a smaller spot they bombard.