The invention relates to a method for preparing anhydrous sodium sulfite by circularly absorbing sulfur dioxide in exhaust gas, comprising the following steps: the exhaust gas containing the sulfur dioxide is pre-washed and re-dedusted, subsequently enters a spray tower so that the sulfur dioxide is absorbed and sodium bisulfite solution is generated; subsequently the sodium bisufite solution reacts with a sodium hydroxide solution to generate sodium sulfite and separates out crystals; the crystals are thickened by a thickener and the mother liquor is removed by centrifuging; the mother liquorand the overflow liquid overflowing out of the upper part of the thickener return to the spray tower and absorb the sulfur dioxide in the exhaust gas; the above steps are circularly conducted to prepare the anhydrous sodium sulfite product. The method adopts a reaction salting-out crystallization process, has short production process flow, low energy consumption and low cost; the absorbing and reaction crystallization system runs circularly and completely closely and generates no wastewater or waste slag; and the method is applicable to the SO2 exhaust gas treatment of various industrial furnaces and coal burning boilers in the industries such as metallurgy, steel, petrifaction, medicals and the like, and can recycle and utilize the SO2 exhaust gas contained in various furnaces.