Coal-fired power plants are the largest sources of mercury in China as well as United States, accounting for nearly 50% of industrial mercury releases. USA consumed much more coal than China before 1987, while no Hg control measures had been taken during this period. There has been lots of background Hg emitted into air system, including those from mining, oil & gas extraction, coal combustion, volcanoes and geothermal et.al. However the coal combustion has been considered as the dominant sources. Since 2005, quite a few coal power plants started adopting mercury control measures based on the powder Active Carbon Injection (ACI) technology in USA, metallic Hg emission to air environment has been thus significantly reduced, but leading to Hg content in fly ash is up to 10 ppm, potentially a Hg pollution source if not disposed properly. Although short terms studies have showed little leachate of Hg occurred from the fly dust, there is a potential that the landfilled or dumped dust may be a possible source for the Hg leachate to contaminate underground water in long term, as Hg is mainly trapped as Hg 2+ or other forms, which are either soluble or minor soluble in water and could go to water environment. Based on this analysis, a more safe and reliable Hg removal technology has been developed and tested. Comparison of Mercury Emissions in USA and