Ta3N5 was potentially a high efficient semiconductor in photocatalytic and photoelectrochemical water splitting but its practical performances were unsatisfactory. The oxygen impurity, which substituted N and acted as an electron donor, was one possible source of the poor photocatalytic and photoelectrochemical activities of Ta3N5. In this study, 24 elements, which substituted Ta and acted as the electron acceptor, were codoped with the oxygen impurity to achieve charge compensation in Ta3N5. Based on the density functional theory calculations, the defect formation energies, electronic structures and carrier mobility were investigated. The results showed that the charge compensation doping method was able to improve the conduction band position of Ta3N5, suggesting that this method was effective to enhance water reduction ability and lower onset potential of Ta3N5. The Ti, Zr and Hf elements were found to be more effective than other elements because they were able to keep the carrier mobility of Ta3N5. Our calculation results agreed well with experiments and provided useful guidance for future investigations of Ta3N5.