The invention provides a synergistic flue gas multi-pollutant removal agent for a dense-phase dry tower desulphurization process and belongs to the technical field of comprehensive flue gas control materials. The synergistic removal agent uses coke breeze as a raw material, surface treatment and continuous roasting are conducted on the coke breeze under a roasting, cooling and nitrogen atmosphere, and finally modified and activated coke breeze is prepared, namely the synergistic removal agent is obtained. By the adoption of the synergistic flue gas multi-pollutant removal agent, desulfurization, N removal, dust removal, heavy metal removal and dioxin removal of flue gas can be simultaneously achieved, the costs for flue gas multi-pollutant removal are effectively reduced, waste recycle of the coke breeze is also performed, and regeneration steps are omitted. Surface treatment and activation are conducted on the coke breeze by filling N2, the problem that the coke breeze easily causes explosion in airtight, relatively high temperature circumstances is effectively prevented, and pit channels formed in the coke breeze surface are also effectively and evenly opened, so that the adsorption performance of the coke breeze is improved by more than 3 times. A preparation method of the removal agent is simple, the adsorption performance is excellent, the waste is turned into waste, and waste recycling is achieved.