The seawater flue gas desulfurization (SFGD) system, as an ideal alternative to traditional limestone-based systems, effectivelycontrols sulfur dioxide (SO2) emissions from coal-fired flue gas while also suppressing mercury (Hg) emissions. However, the reductivenature of seawater has led to concerns regarding the re-emission of mercury on a global scale. In this study, the aeration process of SFGDwastewater was simulated to investigate the effects of pH, system temperature, and the concentrations of and Cl on the re-emissionof elemental mercury (Hg). The objective of this study was to elucidate the migration and transformation characteristics of mercury inSFGD systems. Furthermore, the study investigated the suppression mechanisms of four additives: two precipitants (Na2S, an inorganicsulfide, and TMT-15, an organic sulfide) and two oxidants (NaClO and Fenton reagent). The results demonstrated that S(IV) was theprimary factor promoting Hg0 re-emission, with over 54% of Hg being reduced to Hg at an concentration of 0.05 mmol/L. Concurrently, elevated concentrations of Cl, low temperatures, and heightened pH levels exhibited a substantial inhibitory effect on Hgre-emission. All four additives effectively inhibited Hg re-emission through different mechanisms. Na2S and TMT-15 reacted with Hg inthe liquid phase to form water-insoluble precipitates and chelates, thereby preventing reduction to Hg. NaClO and Fenton reagentsuppressed Hg re-emission by rapidly oxidizing Hg back to Hg and stabilizing it in the liquid phase. They also inhibited Hg reductionby oxidizing reductive ions in the solution. At optimal dosages, the suppression efficiencies of Na2S, TMT-15, NaClO, and Fenton reagentwere 78.1%, 79.9%, 84.8%, and 94.2%, respectively. Compared to precipitants, oxidants such as NaClO and Fenton reagent significantlyreduced the required aeration intensity, demonstrating excellent potential for application in the aeration processes of SFGD wastewatertreatment.