The GGA + U method is applied to calculate the lattice constant and the band gap energy of the As-rich GaBixAs1-x alloy. It is found that the lattice constant almost shows a linear increase as the bismuth fraction increases. The calculated band gap energy is consistent with the experimental data. For the sake of depicting the band gap energy, the valence band anticrossing model is modified. After the modification, a wonderful description can be observed. When the bismuth fraction is 0.324, the band gap energy of GaBixAs1-x decreases to 0 eV. The coupling interaction of the bismuth level with the Г valence band maximum (VBM) of GaAs is much stronger than that of the bismuth level with the Г VBM of GaSb because the atom size mismatch and electronegativity difference between bismuth and arsenide atoms are much larger than those between bismuth and antimony atoms. Additionally, reducing the band gap energy is an inevitable behavior of the bismuth fraction in GaAs, while it is only a special behavior of the nitride fraction, which occurs in GaNxAs1-x when the nitride fraction is not large. The element indium should be the best choice to lower the bismuth fraction by introducing another element to achieve that the spin–orbit splitting energy overtakes the band gap energy.