Carbonation curing cement-based materials can improve the properties of cement products while permanently sequestering CO2, which is considered to be a very promising carbon reduction technology. In this paper, cement pastes with different pore structures were prepared by changing the water-cement ratio (w/c=0.35, w/c=0.4, w/c=0.45) and pre-conditioning time (2, 4, 6, 8, 16, 24, 48 and 72 h), and the influences of pore structure and water content on the carbonation reaction of cement paste were studied. The results show that the carbon sequestration rate of cement paste with different water-cement ratios reaches the maximum when the pre-conditioning time is 8 h, and the carbon sequestration rate increases with the increase of water-cement ratio. At the same time, for cement paste with early hydration (24 h standard curing+8 h pre-conditioning), the influence of water-cement ratio on the pore structure is much greater than the degree of hydration. The cement paste with initial water-cement ratio of 0.45 undergoes 8 h pre-conditioning and then undergoes 8 h carbonization curing. Its carbon sequestration rate, carbonation depth and compressive strength reach 20.35% (mass fraction), 12.49 mm and 61.99 MPa, respectively, which increases the compressive strength by 14.27% compared with the strength of the 28 d standard curing test block (54.25 MPa). The main products of carbonation reaction are CaCO3 and silica gel. The filling of CaCO3 optimizes the pore structure of cement paste, significantly reduces the pores larger than 50 nm, and the main crystal forms of CaCO3 are calcite and aragonite.