Density functional theory (DFT) and Monte Carlo Simulated Annealing (SA) are used to investigate adsorption of CO on TiO2 (110) surface, surface with defects and metal-doped TiO2. First the calculations of structure of TiO2 bulk and TiO2 surfaces (TiO2 (110) surface, surface with defects, metal-doped surfaces) is carried out and they show good agreement with experiments and other Ab-inito calculations. Then CO is adsorbed at acidic sites (Ti and metal) of the surfaces and bond length of CO is observed. The bond length of CO adsorbed increases remarkably (-1.140 A) in comparison with free CO molecule (1.128 A) then it is less stable and easier to react with O2. The surface with defects and Mn-doped surface have the highest ability to lengthen the bond length of CO adsorbed.