The invention belongs to the technical field of dechlorination and particularly relates to a normal-temperature gas-phase dechlorinating agent, a preparation method therefor and an application of thenormal-temperature gas-phase dechlorinating agent. The dechlorinating agent comprises a support and active ingredients, wherein the active ingredients comprise CaO and CuO, the support comprises bentonite and alkali modified fly ash, and the alkali modified fly ash is alkali solution modified fly ash. The preparation method disclosed by the invention comprises the steps of mixing calcium hydroxide, copper oxide, bentonite and the alkali modified fly ash, adding a binder into the mixture, carrying out strip extruding, carrying out drying, and carrying out roasting, thereby preparing the dechlorinating agent. The dechlorinating agent obtained by using the preparation method can achieve a dechlorination function at normal temperatures and has relatively high dechlorination accuracy and penetrating chlorosity.