Density functional calculations have been performed systematically on the electronic structure, the defect formation energy, the crystal structure change and the relative binding energies for the co-doped system of SrTiO3. The La-N, Ta-N and N-N co-doped systems are chosen to simulation the A-O, B-O and O1-O2 three basic selection doping sites for donor acceptor pairs co-doping and hole hole mediated coupling co-doping cases in SrTiO3. An evaluation method with three basic rules for assessing the favorable co-doped dopants for SrTiO3 has been proposed and the favorable co-doping dopant with which is easy to prepare, with high structural stability and high photocatalytic activity among the different types of co-doping on SrTiO3 can be obtained. Our results offer a new path for assessing the favorable co-doping dopants for the band gap engineering of wide band gap semiconductors with different co-doping cases for hydrogen generation. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.