In the present study, seasonal distribution of mercury formation and the impact of eutrophication on the biogeochemicalcycling of the mercury were studied in Hongfng Reservoir. Total mercury concentrations in the water varied from 2.5 to l4 ng/Lwith an average concentration of 6. 9ng/L. The seasonal and spatial distribution of total mer ury could be controlled by the mercurycontaminations. The PH THg ratios were mainly regulated discharged by autochthonous organic materials and redox potential inlake water. The sampling microalgae at Houwu station in May had a large capacity to bind mercury that changed the distributions ofmercury in the reservoir. Dissolved gaseous mercury concentrations were also affected by algal activities. Methyl mercury(MeHg)in the sampling water column at a hyper-eutrophication site of Hongfng Reservoir, demonstrated that most of MeHg was producedin the hypolimnion laye. MeHg profile pattern at the second site, where there is less eutrophication, indicated that MeHg in waterwas largely ascribed to the release from sediment. The distributions of mercury in Hongfeng Reservoir showed that eutrophicationhad a significant impact on transportation and transformation of mercury, especially on methylation of mercury. Eutrophication hasaccelerated formation of methylation of mercury, which may cause serious ecosystem risks to Hongfng Reservoir.