The invention discloses a flue gas desulphurization system and a method for flue gas desulfurization. The system comprises a flue gas desulphurization tower, an ash storage device, a gypsum preparing device and an air induction device, wherein the flue gas desulphurization tower comprises a tower body, a fume extractor, a defrosting device, a rotational flow reaction device, a gas uniformizing device and a multi-functional collecting reservoir, the fume extractor, the defrosting device, the rotational flow reaction device, the gas uniformizing device and the multi-functional collecting reservoir are communicated from top to bottom in sequence, a flue is provided with a dry powder inlet communicated with a dry powder desulfurizing agent spraying device, the multi-functional collecting reservoir is arranged under the gas uniformizing device, the rotational flow reaction device comprises a rotational flow shell and at least one rotational flow chamber provided with at least one swirler inside, each rotational flow chamber is provided with a circular reaction slurry inlet and communicated with the gas uniformizing device, and each swirler comprises an impeller shell, an impeller center shaft and at least five swirl vanes surrounding the impeller center shaft. By the adoption of the system, flue gas desulphurization effect and degree can be improved, space can be saved, a slurrying pool and a slurry precipitation pool are not needed, maintenance is convenient, cost is low, energy is saved, and environment pollution is avoided.