Chemical-looping technology (CLT) can achieve energy efficiency and reduce the environmental pollution and is usually conducted on a fixed-bed reactor. In this paper, the thermodynamic simulations for flue-gas desulfurization (FGD) systems with CLT are carried out using HSC Chemistry software to choose a suitable desulfurizer, control the type and quantities of reaction products, and collect sulfur-containing byproducts with high economic value. The Effingham diagrams are developed to relate the Gibbs free energy of the relevant reactions to the temperature. The fixing-sulfur potential; the reaction degree with CO2, H2O, and CO; and the acceleration effect of removing NOx of different metal oxides in 100 to 300 degrees C are estimated. Compared comprehensively, Mn-based oxides have distinct advantages for flue-gas desulfurization using CLT. Based on calculation results, both low reaction temperatures (T < 400 degrees C) and sufficient H-2 (m(H2)/m(MnSO4) > 4) can effectively prevent the loss of sulfur element. In the regeneration of Mn3O4, if pure O-2 is replaced by diluent air or a low level of oxygen, the formation of trace amounts of MnSO4 can be inhibited. This paper provides ample theoretical basis for Mn-based oxides as active components of desulfurizer and collecting pure SO2 from flue gas through chemical-looping technology.