The photocatalytic properties of TiO2 improved by modifying its surface have attracted more and more attention, because they play an important role in the photocatalytic degradation of greenhouse gases. Based on the fact that the photocatalytic reactions main occur on the catalyst surface, the surface modification becomes an effective method to improve the photocatalyst properties while the reaction mechanism research can give us a clear picture about it. Using the first principle calculations, the formation energies of TiO2 are calculated with doped and codoped by Cu and Ag atoms at different positions of the (001) and (101) surfaces. Comparing the formation energies, the most stable crystal structures are obtained while the electronic structures are calculated. Based on the analysis of the band structures and the density of states of atoms, it is proved that the oxidation activity of the active group formed on the (001) surface is stronger than that on (101) surface, which is more conducive to the improvement of photocatalytic oxidation properties. Meanwhile, the TiO2 compounds codoped by bimetal on the two surfaces have better light response than doped by one species of ions, which is in good agreement with the former experimental results.