Mercury removal in we flue gas desulfurization (WFGD) systems has been widely known to be effective, but removal efficiency is highly susceptible to calcium sulfite (CaSO3), the main byproduct of WFGD systems. Though the influence of CaSO3 on Hg-0 removal from the perspective of Hg-0 re-emission has been studied, systematic studies directly devoted to removal are rare. In this study, the effects of CaSO3 on Hg-0 removal efficiency were investigated using a H2O2/Fe3+ solution as an oxidizing agent. In addition, this experiment was designed to study the influence of operational conditions (temperature and pH), anions (Cl- and NO3-), and combustion flue gas components (SO2 and NO) in WFGD systems on Hg-0 removal efficiency using an H2O2/Fe3+ solution with and without CaSO3. For this experiment, three groups were chosen: 1) the absence of CaSO3, 2) a 0.015% CaSO3 solution, and 3) a 0.075% CaSO3 solution. After the investigation of Hg-0 removal efficiency with single flue gas component, the influence of co-existence gases (SO2, NO, Hg-0) on the simultaneous removal was studied. Results indicated that CaSO3 had adverse effects on Hg-0 removal. For simultaneous removal, the coexistence of SO2 and NO was favorable for Hg-0 removal. Also, Cl- had a desirable effect on NO removal. This study provides new insights into the simultaneous removal of SO2, NO, and Hg-0 in WFGD systems.