The invention discloses a method and system for carrying out zero-emission treatment on high-chlorine desulfurization wastewater and promoting flue gas to be subjected to denitration and mercury removal. The method comprises the following steps: firstly, carrying out reverse refluxing concentration on the desulfurization wastewater and part of the flue gas; after pre-treating the wastewater, pumping the wastewater into a cathode chamber of an electrolysis system, so as to obtain alkaline slurry containing high-concentration chlorine ions; refluxing the alkaline slurry into a pre-treatment coagulation precipitation tank; enabling the high-concentration chlorine ions to penetrate though an anion exchange membrane to enter an anode chamber; electrolyzing in the anode chamber to generate chlorine gas and oxygen gas; after mixing the chlorine gas, the oxygen gas, anode electrolyte and air, conveying a mixture into a prepositioned SCO system to participate in oxidization of Hg<0> and part ofNO. According to the method disclosed by the invention, high-chlorine desulfurization wastewater treatment and the denitration and mercury removal of the flue gas are subjected to ectopic coupling, so that the zero-emission aim of the desulfurization wastewater is realized, the problem of Hg<0> pollution also can be solved through simultaneous oxidation and the content of NO2 in the flue gas is improved; denitration reaction of rapid SCR (Selective Catalytic Reduction) is promoted and simultaneous denitration and mercury removal of the flue gas are realized.