[en] The paper describes results of a theoretical study of the electronic structure of the capped finite-length single-walled carbon nanotube (5, 5) under an applied electric field in the range from 0 to 0.5 V/Å. Clear oscillations of an ionization potential, electron affinity, gap energy and an effective work function on the length of the nanotube are presented. An applied electric field leads to the energy gap decrease and the work function increase. An estimation of the electron emission current density changes is revealed taking into account the work function dependence both on the nanotube length and the strength of the electric field