We report a DFT study of interaction between the Ru complex sensitizer [Ru(dcbpy)(2)(NCS)(2): dcbpy = 4,4'-dicarboxy-2,2'-bipyridyl] (N3) and iodide ion under the influence of different deprotonation situations. There are two kinds of interaction mechanisms: iodide ion interacts with metal-center Ru atom or carboxyl, derived from the natural charge distribution analysis. The calculation indicated that there were several stable intermedium forms in different deprotonation degree. The stability of these intermedium forms would be perturbed gradually while the number of eliminated protons increased. It can be predicted that in the initial period of absorption and injection as well as the dissolve process where the deprotonation was demanded, the dye will not attacked by the iodide ion in solution extensively. Additionally, dye with more carboxyls will reduce the activity of redox reaction and more obstacles are required to be overcome before or during the redox reaction. The comparison of natural charge between isolate N3 and N3 with iodide ion intermedium (N3I(-)) showed the iodide ion attacking made the charge contribute on N3 molecule more negative, nevertheless the N3I(-) still has ability to attract another iodide ion. The attacking of iodide ion will also influence the electronic transition and absorption properties through the analysis of the frontier molecular orbitals and the densities of states. The results reported in this paper give us the guidance to carry out the further investigations about the dye regeneration process.