By using the Green's function method the electronic state of the CuO2 plane of a high-T(c) oxide superconductor with one O2- vacancy and one additional electron has been investigated. The basis contains a vacancy-centred s-type function. Account is taken of charge transfer to the neighbours. The energy of localized states between the top of O-valence band and upper Hubbard component is obtained as a function of sp resonance integral. The F+ centre ground state is stable.