The application relates to a method and system for controlling the mercury emissions from the coal-fired thermal processes, in particular to a method of controlling the mercury emission from an industrial device, and also relates to a method of removing the mercury from a gas flow containing the mercury and used for the industrial device. The method comprises the steps of jointly mixing a first coal and a second coal to provide a coal feedstock containing the iodine content, wherein the first coal has the iodine of the natural high concentration and the second coal does not have the iodine orthe iodine lower than the concentration of the first coal; contacting the provided coal feedstock with an iodine containing additive to form a processed feedstock material; generating the mercury-containing gas flow containing the mercury and the iodine of the gaseous phases from the processed feedstock material; and removing at least 50% or more mercury from the mercury-containing gas flow.