Electronic structures and optical properties of intrinsic α-Bi2O3, La-doped, oxygen vacancy doped, and co-doped systems were studied by first-principles method based on density functional theory, in order to obtain α-Bi2O3 photocatalytic materials with excellent performance. The results show that the structure of the doped system is less distorted, and the oxygen vacancy (VO) doped and La-VO co-doped systems have band gaps of both valence band and conduction band shifted down and impurity energy levels introduced in band gaps, indicating that doping can reduce the energy required for electron excitation from valence band to conduction band, which is beneficial to the electron leap. In particular, the La-VO co-doping makes the impurity energy level close to conduction band bottom compared to the oxygen vacancy single doping, and this tendency may make the recombination defect more likely to be the capturing center of photogenerated electrons than the recombination center of photogenerated electron-hole pairs. At the same time, La-VO co-doping leads to the increase of the curvature of band bending near the conduction band bottom, that is, the enhancement of the dispersion relationship, which reduces the effective mass of electrons and accelerates the movement of electrons. Therefore, La-VO co-doping can greatly improve the effective separation of photogenerated electron-hole pairs. On the other hand, La-VO co-doping, while significantly extending the visible light absorption range, also greatly enhances the visible light absorption intensity. Therefore, La-VO co-doping can effectively improve the photocatalytic activity of α-Bi2O3. This study provides a new idea for improving the performance of other photocatalytic materials by using rare earth ion doping.