The invention discloses a water treatment device utilizing flue gas waste heat. Raw water enters a pretreatment device, the water outlet end of the pretreatment device is connected with the water inlet end of a regulation tank, the water outlet end of the regulation tank is connected with the water inlet end of a heat exchanger, and the water outlet end of the heat exchanger is connected with the water inlet end of a middle water tank. The heat exchanger is located in front of a flue gas inlet of a desulfurizing tower, flue gas enters a flue gas inlet of a dust remover, a flue gas outlet of the dust remover is connected with a flue gas inlet of the heat exchanger, and a flue gas outlet of the heat exchanger is connected with the flue gas inlet of the desulfurizing tower. The water inlet end of a second water pump is connected with the water outlet end of the middle water tank, the water outlet end is connected with the water inlet end of a membrane distillation device, and the water producing end of the membrane distillation device is connected with a produced water tank. The invention further provides a water treatment method utilizing flue gas waste heat. The water treatment device has the advantages that power plant waste heat utilization and a membrane distillation process are combined, the flue gas before desulfurizing is adopted as a heat source of a membrane distillation water treatment system, the flue gas waste heat is fully utilized while the membrane distillation water treatment process is completed, the flue gas temperature of a desulfurizing system is reduced, and the water consumption for desulfurizing can be remarkably decreased.