The invention discloses a method for removing mercury from smoke in a coal fired power plant and a mercury removing agent used by the same. In the term of the weight percent, the mercury removing agent is prepared from cobalt oxide and copper chloride in a mass ratio of (5-10):1000 through mixing. The mercury removing agent adopted in the invention can be directly used in a limestone- gypsum wet desulphurization system, is simple in use and convenience for use without reconstructing the traditional equipment and is low in cost; and the method for removing mercury by using the mercury removingagent has the advantages of high mercury removing efficiency, difficulty in corrosion to the device, and no generation of secondary pollution, can be used for oxidizing NO in the smoke into NO2 easily dissolved into water, and realizes the effect of removing mercury and NOx simultaneously.