Mercury is a first order pollutant in the world. It is one of the widespread heavy metal toxicants in water. Mercury pollutants come into the water in three forms, metal, inorganic mercury compound and organic mercury compound. Inorganic mercury could be turned into organic mercury by microbes in the water, and its toxicity increases. Mercury is an accumulative toxic substance. It does great harm to human health. Inorganic mercury and organic mercury mainly damage the central nervous system and the kidneys.