The Eu-doped Cu(In, Eu)Te_2 semiconductors with chalcopyrite structures are promising materials for their applications in the absorption layer for thin-film solar cells due to their wider band-gaps and better optical properties than those of CuInTe_2. In this paper, the Eu-doped CuInTe_2(CuIn_(1-x)Eu_xTe_2, x = 0, 0.1, 0.2, 0.3) are studied systemically based on the empirical electron theory(EET). The studies cover crystal structures, bonding regularities, cohesive energies, energy levels,and valence electron structures. The theoretical values fit the experimental results very well. The physical mechanism of a broadened band-gap induced by Eu doping into CuInTe_2 is the transitions between different hybridization energy levels induced by electron hopping between s and d orbitals and the transformations from the lattice electrons to valence electrons for Cu and In ions. The research results reveal that the photovoltaic effect induces the increase of lattice electrons of In and causes the electric resistivity to decrease. The Eu doping into CuInTe_2 mainly influences the transition between different hybridization energy levels for Cu atoms, which shows that the 3d electron numbers of Cu atoms change before and after Eu doping. In single phase CuIn_(1-x)Eu_xTe_2, the number of valence electrons changes regularly with increasing Eu content,and the calculated band gap E_g also increases, which implies that the optical properties of Eu-doped CuIn_(1-x)Eu_xTe_2 are improved. The Eu-doped Cu (In, Eu) Te 2 semiconductors with chalcopyrite structures are promising materials for their applications in the absorption layer for thin-film solar cells due to their wider band-gaps and better optical properties than those of CuInTe_2. In this paper , the Eu-doped CuInTe 2 (CuIn 1- (1-x) Eu x Te 2, x = 0, 0.1, 0.2, 0.3) are studied systematically based on the empirical electron theory (EET). The studies cover crystal structures, bonding regularities, cohesive energies, The physical values ​​of the broadened band-gap induced by Eu doping into CuInTe_2 are the transitions between different hybridization energy levels induced by electron hopping between s and d orbitals and the transformations from the lattice electrons to valence electrons for Cu and In ions. The research results reveal the photovoltaic effect induces the increase of lattice electrons of In and causes th The Eu doping into CuInTe_2 mainly influences the transition between different hybridization energy levels for Cu atoms, which shows the 3d electron numbers of Cu atoms change before and after Eu doping. In single phase CuIn_ (1-x) Eu_xTe_2, the number of valence electrons changes regularly with increasing Eu content, and the calculated band gap E_g also increases, which implies that the optical properties of Eu-doped CuIn_ (1-x) Eu_xTe_2 are improved.