The invention discloses a low-energy-consumption and ultraclean-emission flue gas desulfurization method and device and belongs to the field of flue gas pollution treatment. According to the invention, desulfurization slurry is divided into two independent desulfurization spraying slurry circulating systems and a three-circulation desulfurization process of a double-slurry collection device (a slurry tank/box), double-slurry density and control of pH values of slurry of different regions is adopted so that the aims of lowering energy consumption and meeting the requirements of ultraclean or near-zero emission of PM and SO2 are realized. The double-slurry tank/box is arranged, the different slurry densities of the double-slurry tank/box is controlled, the pH values of the slurry in the different regions are controlled and the two independent slurry circulating systems are formed, so that the aims that the solid content of desulfurized pure flue gas liquid drops is lower than 10% and the system desulfurization efficiency is more than 99% are realized; and a slurry tank outside a tower is arranged at a high liquid level and fewer spraying layers are arranged so that the aims of lowering the power of a circulating pump and reducing the operation power consumption of the desulfurization are realized.