The invention discloses a method for preparing iron-doped nitrogen-doped nanometer titanium dioxide powder. The preparation method comprises the steps of preparing titanium tetrachloride raw material to be hydrosol, aging the hydrosol, adding water for dilution, doping water-soluble iron salt, raising temperature to hydrolyze sol and produce precipitate, filtering the precipitate, using water to wash the precipitate, drying the precipitate, obtaining iron-doped nanometer titanium dioxide powder, mixing and then ball-milling nitrogen salt and the iron-doped nanometer titanium dioxide powder, calcining the ball-milled powder, and cooling the powder to obtain the iron-doped nitrogen-doped nanometer titanium dioxide powder. The preparation method combines a chemical method with a physical method so as to allow iron to uniformly enter a crystal lattice structure of titanium dioxide on the one hand, and to uniformly distribute nitrogen in surface layers of nanometer particles, particularly non-crystallization layers on the other hand. The iron-doped nitrogen-doped nanometer titanium dioxide powder can improve the photocatalysis efficiency of titanium dioxide on the one hand, and can expand the photoresponse wavelength of titanium dioxide so as to greatly improve photocatalysis properties.