Absorption spectra of BiSbO₄ are studied. The electronic structure calculated by the DFT shows that BiSbO₄ is a semiconductor, with direct band gap 2.96 eV, which is consistent with UV-visible diffuse reflectance experiment. The host lattice emission band is located at 440 nm under VUV excitation. Eu³⁺ and Pr³⁺ doped samples have high luminescence efficiency in emitting red and green light, respectively. From the partial density of states, Eu³⁺ doped emitting spectrum, and the host crystal structure parameters, the relationship between structure and optical properties is discussed. It is found that the Eu³⁺ ions occupied Bi³⁺ sites, and there could be an energy transfer from Bi³⁺ ions to RE³⁺ ions.