Calcium looping process is a kind of cost-effective and high-efficiency CO2 capture technology. A certain amount of fresh calcium based sorbent should be supplemented to the process and corresponding amount of spent sorbent is discharged. It is of significant to realize in situ reutilization of such a quantity of spent calcium based sorbent. A dual-fixed bed reactor was employed to prepare the spentlimestone and investigate the cyclic carbonation conversions of spent limestone after self-reactivation. XRD, SEM and N2 adsorption analysis were employed to discuss the mechanism that self-reactivation improves the CO2 capture capacity of spent limestone. The results showthat when placed in a constant humidity environment, spent limestone can absorb the H2 O in the air to form Ca(OH) 2 and go on toform calcium hydroxide hydrate when the value of water absorption φ is 100%. The limit value for φ is 130%. CO2 capture capacity of thespent limestone is dramatically enhanced after self-reactivation, which is proportional to φ. Compared with CaCO3, the CO2 capture capacity of spent limestone is much more sensitive to φ. When φ is 130%, the CO2 capture capacity of the spent limestone after self-reactivation is even higher than that of the fresh limestone. The microstructure analysis results show that due to the sintering occurred under hightemperature calcination, the CaO grain size in calcined limestone increases from 41.9 nm to 72.2 nm. The micro-pores are blocked. Thepore volume and BET surface area decrease dramatically. After self-reactivation, the CaO grain size in the calcined limestone obviouslydecreases, and plenty of pores are regenerated on the surface. When φ is 130%, the CaO grain size decreases to 35.1 nm, the pore volume and BET surface area are recovered to 70.5% and 107.6% those of the calcined fresh limestone, especially the pore volume that distributed in 10-100 nm is regenerated dramatically. Therefore, the CO2 capture capacity of spent limestone can be enhanced by self-reactivation. The self-reactivation process can accelerate the attrition rate of spent limestone. However, even when φ is 100%, the diameter ofthe sorbent particle only decreases by 0.55% per hour. To sum up, the spent limestone after self-reactivation can sufficiently be used assupplementary sorbent instead of fresh limestone in calcium looping process for CO2 capture.