The disclosure provides a mercury removal system for a coal-fired power plant comprising: a mercury content monitoring system configured to monitor a mercury concentration in flue gas; a fly ash collecting device configured to collect fly ash from an electrostatic precipitator in the coal-fired power plant; a modifying device configured to be supplied with the collected fly ash and prepare a mercury sorbent from the fly ash; a sorbent injector configured to inject the mercury sorbent into flues of the coal-fired power plant so as to mix and contact with the flue gas in the flue and adsorb the elemental mercury in the flue gas. Thus, the concentration of the mercury pollutant emission is decreased.