  Using the strong coupling diagram technique equations are derived for hole
Green's functions of the three-band Hubbard model, which describes Cu-O planes
of high-$T_c$ cuprates. The equations are self-consistently solved in the
approximation, in which the series for the irreducible part in powers of the
oxygen-copper hopping constant is truncated to two lowest-order terms. For
parameters used for hole-doped cuprates the calculated energy spectrum consists
of lower and upper Hubbard subbands of predominantly copper nature, oxygen
bands with a small admixture of copper states and the Zhang-Rice states of
mixed nature, which are located between the lower Hubbard subband and oxygen
bands. The spectrum contains also pseudogaps near transition frequencies of
Hubbard atoms on copper sites.
