Finding an efficient adsorbent has been a dilemma for almost all adsorption and desorption processes. The stronger affinity of an adsorbent induces the deeper potential well after adsorption which needs to consume more extra energy to regenerate, like heating. A breakthrough could take place if the conversion between adsorption and desorption of a sorbent requires no additional costly energy. This paper reports the research progress of a novel water-driven CO_2 adsorbent, which can capture CO_2 when surrounding is dry, while release CO_2 when surrounding is wet. The adsorption/desorption process is only triggered by controlling the amount of water molecules, without the need of additional heat or electrical energy to regenerate. This paper summarizes the development path and the disruptive mechanism of this new energy-saving adsorbent, as well as shed light on the future study of the humidity-swing CO_2 adsorbent. In the paper, we first demonstrate the severity of global warming and the urgency of air capture CO_2. Next, we explain the underlying mechanism and working process of the humidity-swing CO_2 adsorbent, as well as the advantages and preparation methods of the air capture CO_2 adsorbent are summarized. Then, the significance of the principle of the surface chemistry phenomenon is elaborated. Last, the direction of development of the novel CO_2 adsorbent is pointed out. The low-cost and high-efficiency CO_2 capture technology, for the first time makes the larger-scale production of capturing CO_2 from ambient air has become possible. Moreover, the underlying mechanism has a significant impact on the study of surface chemistry and nano-confined water molecules. The discovery has wide potential applications, including on design possibility for more efficient energy conservation adsorbent against traditional energy-consuming sorbent material. Therefore, this review paper is extremely important for the future study of the relevant research.