Mercury exists in three valence states in the environment (Hg º, Hg¹ ,Hg²), Its emissions mainly come from coal-fired power plants, industrial boilers, waste incineration, and some industrial processes Due to the toxicity, persistence, and bioaccumulation effects of mercury, the pollution of heavy metal mercury has received increasing attention with the strengthening of people's health awareness. The US Environmental Protection Agency (EPA) has passed the Mercury Clean Air Act (PS-12A and Part 75) to control mercury emissions from coal-fired power plants and mandate online monitoring of mercury emissions from coal-fired power plants.