Density functional theory (DFT) is used to investigate properties of TiO2 (110) surface, surface with defects and metal-doped TiO2. The results of calculations of structure of TiO2 surface have been shown in good agreement with those of experiments and other ab-initio calculations. The differences of band structure between TiO2 (110) and TiO2 surface defected show that visible light can excite surface with defects easily. The authors also investigate density of states (DOS) of metal-doped surface (Li, Ca, Sc, Y, Mo, Mn, Fe, Co, Ni) and find that the Mo-doped surface has very small band gap (-0 eV). This surface may have higher photo - chemical activity in visible light.