Disclosed are a system and a method for desulfurization and denitrification of an alumina calcination flue gas, and a use. The system comprises an ozone generator, a red mud pre-impregnation slurry scrubbing tower, and a red mud pre-impregnation tank and a red mud pre-impregnation clear liquid scrubbing tower. NOx in a flue gas is oxidized into a high valence oxynitride by ozone, and with the red mud as an absorbent, the synergistic absorption of SO2 and NOx in the flue gas is achieved, while the dealkalization of the red mud is achieved. By means of the synergistic catalytic oxidation of metal ions such as Fe3+ in a red mud slurry and ozone, the synergistic absorption of sulfur and oxynitride is prompted; and the use of a structure of staged absorption in two towers overcomes the problem of the difficulty in absorbing NO2 with a low O3/NOx molar ratio.