We performed first-principles calculations of Mn-doped structures in which Mn atoms substitute Ti atoms.Formation energy,density of state and magnetic moment are calculated for Mn ions doped TiO₂(001) and F-TiO₂(001) thin films.In all doping configurations adsorption of F atoms on surface lowers formation energy of TiO₂:Mn system significantly.Magnetic moments of Mn ions are reduced,whereas those of O atoms on surface are increased.Magnetic moment of O atoms is mainly derived from spin polarization p_x and p_y orbitals.F adsorption promotes doping of Mn atoms and improves stability of structure,magnetism,and metallicity to a certain extent.