The invention provides a method for concentrating, converting, recovering and processing light concentration SO2 (sulfur dioxide) flue gas. The method comprises the steps of: purifying and concentrating SO2, desorbing the SO2 and converting the SO2. The method comprises the following steps of: absorbing the light concentration SO2 flue gas by citrate, then desorbing the light concentration SO2 flue gas to discharge higher concentration SO2, fully contacting Na2S (sodium sulfide) solution with the desorbed higher concentration SO2, so that the higher concentration SO2 is converted into NaHSO3 (sodium hydrogen sulfite) and Na2S2O3 (sodium thiosulfate), controlling an appropriate pH value and temperature, performing a self-oxidation reduction reaction on NaHSO3 and Na2S2O3 to generate elemental sulfur and sodium sulfate, and performing liquid-solid separation to obtain the elemental sulfur solid and sodium sulfate solution; and crystallizing the sodium sulfate from the solution through a crystallization method, and reducing by coke oven gas or coke to produce sodium sulfide, and returning to the adsorbing procedure. By the method, the processing effect and economic efficiency of the light concentration SO2 can be increased; the sulfur in the SO2 is effectively used through an elemental sulfur method; a new thought for processing the light concentration SO2 flue gas is provided; the whole technology is a closed circulation system; the problem of processing wastes and waste water does not exist; and secondary pollution is avoided.