A flue gas desulfurization-denitration process, comprising the following procedures: 1) afterheat recovery procedure: the temperature of the flue gas is lowered to below 50°C in a heat exchange recovering way, and afterheat recovery is carried out; 2) desulfurization-denitration procedure: the cooled flue gas enters into an absorption tower, sulfur dioxide and/or nitrogen oxides therein are absorbed by a desulfurization-denitration solution, and the said desulfurization-denitration solution is a composite solution containing polyol and/or polymeric polyol; 3) regeneration procedure of desulfurization-denitration solution: in a regeneration tower, the desulfurization-denitration solution with absorbed sulfur dioxide and/or nitrogen oxides releases the sulfur dioxide and/or nitrogen oxides by ways of heating and/or gas stripping and/or vacuum regeneration, and the desulfurization-denitration solution after regeneration is recycled for use; 4) sulfur dioxide and/or nitrogen oxides concentration procedure: in a concentration tower, sulfur dioxide and/or nitrogen oxides released by the regeneration procedure of the desulfurization-denitration solution are concentrated into a product of sulfur dioxide and/or nitrogen oxides with a higher purity; wherein the sulfur dioxide and/or nitrogen oxides concentration procedure is specifically as follows: a mixed gas released by the regeneration procedure of desulfurization-denitration solution, which contains sulfur dioxide and/or nitrogen oxides, enters from a middle section of the concentration tower, contacts with the condensed water from the top of the concentration tower in a counter-current way to condense water vapor in the mixed gas, the mixed gas with water vapor removed flows out of the top of the concentration tower; water vapor enters from the bottom end of the concentration tower, contacts with the condensed water in a counter-current way, residual sulfur dioxide and/or nitrogen oxides in the condensed water are extracted by the water vapor, so as to turn the condensed water into distilled water, which flows out of the bottom of the concentration tower and is recycled. 1) afterheat recovery procedure: the temperature of the flue gas is lowered to below 50°C in a heat exchange recovering way, and afterheat recovery is carried out; 2) desulfurization-denitration procedure: the cooled flue gas enters into an absorption tower, sulfur dioxide and/or nitrogen oxides therein are absorbed by a desulfurization-denitration solution, and the said desulfurization-denitration solution is a composite solution containing polyol and/or polymeric polyol; 3) regeneration procedure of desulfurization-denitration solution: in a regeneration tower, the desulfurization-denitration solution with absorbed sulfur dioxide and/or nitrogen oxides releases the sulfur dioxide and/or nitrogen oxides by ways of heating and/or gas stripping and/or vacuum regeneration, and the desulfurization-denitration solution after regeneration is recycled for use; 4) sulfur dioxide and/or nitrogen oxides concentration procedure: in a concentration tower, sulfur dioxide and/or nitrogen oxides released by the regeneration procedure of the desulfurization-denitration solution are concentrated into a product of sulfur dioxide and/or nitrogen oxides with a higher purity;