The invention provides a flue gas desulphurization device and desulphurization method. The flue gas desulphurization device comprises a limestone slurry preparation system, a flue gas absorption system, a gypsum slurry dehydration system, a waste water treatment system and an electronic control system. According to the flue gas desulphurization device, flue gas important parts, namely a gypsum slurry dehydration system taking a disc type dehydrator as a core, the waste water treatment system and the electronic control system, are integrated and three-dimensionally arranged in one technology comprehensive building, other technological stages in flue gas desulphurization are arranged on ground at the periphery of the technology comprehensive building tightly around the technology comprehensive building, structure is compact, layout is reasonable, space resource is fully utilized, floor space is saved, labour intensity in equipment running check is reduced, engineering construction investment is saved, and energy consumption of the flue gas desulphurization device is greatly reduced.