The invention relates to an improved process for performing ammonium sulfite pulping by using a sulfur-containing flue gas absorber, which comprises the following steps: (1) performing desulphurization on flue gas by using ammonia water, wherein the flue gas is sulfur-containing flue gas; and (2) performing ammonium sulfite pulping during papermaking by using sulfurous acid mixed solution obtained after the desulphurization. In the improved process, a high-efficiency flue gas absorption system is adopted; and the obtained ammonium sulfite is used for ammonium sulfite pulping in papermaking industry. The scheme of the invention not only minimally reduces the environmental pollution, but also recycles the resources. The improved process is particularly suitable to be used in a paper mill with a self-owned power plant.