A mixed absorbent of N,N'-bis(2-hydroxyethyl) piperazine (BHEP) and sulfolane (SUF) was developed for reducing energy consumption in desulfurization. The effects of SUF dosage and inlet SO2 volume concentration on absorption-desorption performance and regeneration energy consumption were investigated, and the synergistic mechanism between SUF and BHEP for SO2 absorption by the BHEP-SUF system was also explored. The results demonstrated that with an increase in SUF dosage, both the saturated absorption capacity (AQ) and effective absorption capacity (EQ) increased first and then decreased, while the regeneration energy consumption (Q) exhibited a continuous decrease. The higher the inlet SO2 volume concentration, the greater AQ and EQ, and the lower the regeneration energy consumption. When 5wt% SUF was added to the aqueous solution of 20wt% BHEP-4.5wt% H2SO4, the AQ and desorption efficiency (DE) were increased by 2.4% and 3.7%, respectively, after four recycling runs. Furthermore, Q was reduced by 9.0%, and the condensate was decreased by approximately 22.9% during desorption. This implied that the decrease in energy consumption was primarily attributed to the reduction in water vaporization induced by SUF. 13C NMR and 1H NMR results indicated that the protonation reaction between BHEP and H+ was not affected by SUF. Molecular dynamics simulation results showed that SUF attenuated the self-agglomeration of BHEP molecules, thereby enhancing their reactivity toward SO2. The BHEP-SUF mixed absorbent not only possesses a high SO2 absorption capacity, but also achieves low regeneration energy consumption, thus showing great application potential for SO2 capture.