The invention discloses a method for removing elemental mercury in coal-fired flue gas. Removing is carried out in a spray absorber. A prepared absorbent is sprayed from the upper portion of the spray absorber for carrying out spraying on coal-fired flue gas introduced in from a smoke opening in the lower portion of the spray absorber, elemental mercury in the coal-fired flue gas sufficiently reacts with the absorbent, and conversion from the elemental mercury to divalent state mercury is achieved; the absorbent comprises an oxidation additive and a magnetic catalyst which have the mass ratio being 2-5:1, the oxidation additive is any one of or the combination of two or more of potassium peroxymonosulfate, sodium persulfate, sodium perborate and sodium percarbonate, and the catalyst is any one of or the mixture of two or more of bismuth ferrite, cobalt doped bismuth iron acid, cobalt/lanthanum doped bismuth ferrite, cobalt/strontium doped bismuth ferrite, cobalt/rubidium doped bismuth ferrite. The method has the advantages that the absorbent utilization rate is high, the catalyst can be repeatedly used, secondary pollution is avoided, operation is easy and convenient, running is stable, the product is easy to treat, and application and popularization are convenient.