The invention relates to a semidry method flue gas desulfurization method belonging to the field of environmental engineering. In the method, coking waste water completely or partially replaces semidry method flue gas desulfurization humidifying water; as a good alkaline absorbent, the effective ammonia component in the coking waste water can absorb SO2 in flue gas, and simultaneously, since the ammonia participates in the desulfurization reaction, the use level of lime can also be reduced. In the high-efficiency semidry method flue gas desulfurization method, wastes are used to treat wastes and organic and inorganic matters are combined. The method not only reduces the use level of the humidifying water and the lime but also comprehensively utilizes valuable components in industrial waste water, thereby achieving the goal of using the wastes to treat the wastes.