The composition of desulfurization slurry is complex due to the recycling utilization of the slurry, in particular the halogen elements are easy to accumulate in the slurry and  difficult to be removed. Oxidated mercury is water soluble and is easy to be removed by wet flue gas desulfurization (WFGD) system, however, the absorbed mercury in the desulfurization slurry has the problem of secondary release. Therefore, the influence of halogen elements on Hg emission in WFGD system was systematically studied in the lab-scale by on-line monitoring and the influence of reaction temperature, halogen species, halogen concentrations, and reaction pH  on mercury release were investigated. The mechanism of mercury emission behavior was also simulated. The results indicate that the mercury emission is inhibited by halogen elements in the increasing order of Cl<Br<I. Increasing the reaction temperature is conducive to reducing the release intensity of mercury where the over 20% decrease is achieved with the temperature increasing from 40 ℃ to 60 ℃. Increasing the concentrations of halogen elements results in a remarkable inhibition of mercury emission. When the concentrations of Cl, Br, and I increase from 5 mmol/L to 50 mmol/L, mercury emission are reduced by 23.5%,53.8%,and 62.8%, respectively. After increasing the reaction pH, the reduction potential of the reaction system decreases, which can weaken the protonation of the intermediate products, and is conducive to reducing the intensity of mercury release. The addition of halogen element can alter the pathway of mercury emission and mercury and halogen will form a series of complexes, reducing the contact between mercury and reducing substances in the system to form unstable intermediate HgSO3, thus reducing the release intensity of mercury.