The invention discloses a device and a method for capturing carbon dioxide in flue gas, and relates to flue gas treatment. The device is provided with a circulating fluidization reaction absorption tower, a bag-type dust collector, an absorbent bin, a material circulating chute and a bin pump; the tower is provided with a mixing area, a venturi acceleration area and a circulating fluidization reaction absorption area; the inlet of the mixing area is connected with an inlet flue of the tower; the mixing area is connected with the absorption area through the venturi acceleration area; the outlet of the absorbent bin is connected with an absorbent inlet of the mixing area; a flue gas outlet of the absorption area is connected with the bag-type dust collector through an outlet flue of the tower; a material outlet of an ash hopper arranged on the lower part of the bag-type dust collector is connected with the mixing area through the material circulating chute; and a purified gas outlet of the bag-type dust collector is connected with a chimney. The flue gas enters the tower through the inlet flue of the tower, is premixed with an absorbent from the absorbent bin and materials circulating back from the material circulating chute in the mixing area, and is primarily decarbonized; the flue gas passes through the venturi acceleration area and enters the absorption area; and the flue gas enters the bag-type dust collector through the outlet flue of the tower to become clean flue gas, and the clean flue gas enters the chimney through a draught fan.