The interaction of the implanted nitrogen and iron atoms on the anatase TiO 2 (101) surface was investigated by the first-principles calculations. Substitutional and interstitial configurations of Fe doping, with and without N atom, at different sites were considered. The formation energies of the cases were calculated, and the results suggested that a larger energy barrier blocked the transfer of Fe atom from the surface to body. A synergetic effect was observed taking place between the co-doped N and Fe atoms. A comprehensive analysis of electronic structure and state density revealed that the property of TiO 2 changed from semiconductor to half-metallic. Finally, on the meliorated anatase TiO 2 (101) surface (M-S (101)), the adsorption energies (ΔE ads ) of diatomic (CO), triatomic (N 2 O, CO 2 ) and polyatomic (NH 3 and CH 4 ) gases were obtained and compared with the former experimental and theoretical results.