Based on a lab-scale wet flue gas desulfurization scrubber, mercury re-emission and migration during the desulfurization process were experimentally investigated under simulated air and oxy-fuel combustion atmospheres. The effects of O-2, CO2, and metal ions were especially studied. The results show that adding O-2 to a pure N-2 atmosphere can remarkably enhance He re-emission because of an obvious decline of pH values, while the introduction of 75% CO2 to N-2 atmosphere results in a limited He re-emission because of a lower pH drop. The re-emission of He is found to be slightly suppressed with increasing O-2 concentration from 3 to 9% under air atmosphere and from 3 to 6% under oxy-fuel combustion atmosphere. Moreover, a further increase of O-2 concentration to 12% has no significant impact on He re-emission under these two atmospheres. At a higher CO2 concentration, less mercury is re-emitted to the gas phase and more mercury is maintained in the solid phase. Under N-2 atmosphere, metal ions such as Fe2+, Mn2+, and Ni2+ can intensify He re-emission in the order of Fe2+ > Ni2+ > Mn2+. However, the reduction of mercury is inhibited by metal ions under air and oxy-fuel combustion atmospheres. The inhibitory effect of Fe2+ is intensified with increasing CO2 concentration. It can be concluded that the existence of Fe2+ is more conducive to mercury control under oxy-fuel combustion atmosphere than that under air atmosphere.