Bond relaxation and the associated electronic energies mediate the properties of a substance, and therefore, doping could be the effective means for such purpose. With the aid of first principle calculations and experimental observations, we examine four co-doped specimens (Ta–N1, Ta–N2, Ta–N3, Ta–N4) with different Ta and N co-doped positions, and show that Ta or N addition could modulate the electronic, optical and photocatalytic responses of TiO2 for photocatalysts applications. Results show that, Ta–O bonding not only reduces the electronic transition energies but also increased the carrier mobility of impurity level in Ta-doped and Ta–N2, Ta–N3, and Ta–N4 co-doped TiO2 specimens, while the impurity level disappears and the band gap reduces by 0.46 eV in Ta–N1 co-doped specimen due to the forming Ta–N bonding. Most strikingly, Ta–N co-doped TiO2 have twofold photocatalytic ability better than pure TiO2 under visible light excitation.