Abstract: Methylmercury is the most toxic form among mercury compounds in the aquatic ecosystem, and poses health risks to organisms through the food chain.The effective control of methylation processes of mercury is an active research field in environmental chemistry and toxicology.Selenium(Se) has a significant suppression effect on the methylation processes of mercury(Hg).Therefore, it will be beneficial to the prevention and control of mercury contamination to clarify the speciation characteristic of mercury and the interaction mechanisms between mercury and selenium in the aquatic ecosystem.Mercury toxicity is closely associated with the levels of selenium in organisms, the interaction between Hg and Se are mainly embodied in the formation of insoluble compounds to contribute mercury demethylation or methylmercury directly ruled out by inhibition of biological a selenium related enzyme, which inhibits the toxic effect of mercury.In this paper, the speciation and distribution characteristics of mercury and selenium in the aquatic ecosystem and their interaction mechanisms were reviewed.Meanwhile, the reasonable addition of selenium compounds into water will be an effective way to inhibit the methylation processes of mercury in organisms.The development direction for the studies of interaction mechanisms between mercury and selenium and its physical effects in organisms were also reviewed.