The invention discloses a hydration-reactor-loaded device and method for CO2 cyclic capture through a composite absorbent. The hydration-reactor-loaded device comprises a calcination-reduction reactor(1), a condenser (2), a hydration reactor (3), an air reactor (4), a carbonation reactor (5), a heat exchanger (6) and connecting pipelines between all the parts. According to the method for CO2 cyclic capture, Ca(OH)2 and CaO in the calcium-copper-based composite absorbent react with smoke entering the carbonation reactor, and CO2 is captured; a solid product reacts with CH4 led into the calcination-reduction reactor in the calcination-reduction reactor, and the high-concentration CO2 is generated; part of a reacted solid body enters the hydration reactor to improve the pore structure and enhance the reaction activity; and the activated composite absorbent enters the air reactor to complete regeneration of a copper-based oxygen carrier. The CO2 in the smoke is captured in a low-energy-consumption mode by applying the calcium cycle coupling chemical chain process, and meanwhile the absorbent carbonation performance degradation is restrained through a hydration reaction.