To compare and analyze the impact of fly ash properties on the differences in carbonation capacity, coal-fired power plant fly ash and circulating fluidized bed fly ash were studied as research subjects. Experiments on carbon sequestration and alkalinity reduction in fly ash slurry under different temperature and pressure conditions were conducted, and the pH changes in the slurry during the mineralization of CO2 by fly ash were measured. Analytical methods such as X-ray diffraction（XRD）, scanning electron microscopy（SEM）, ion chromatography, and simultaneous thermal analysis were used to study the differences in physical and chemical properties before and after the reaction, as well as the carbon fixation capacity. The research results indicate: (Ⅰ) Under the same conditions, CFB fly ash exhibits a higher alkalinity reduction efficiency compared to coal-fired power plant fly ash. Within a reaction time of 75 minutes, the pH of CFB fly ash slurry can be reduced to below 7, while coal-fired power plant fly ash requires approximately 175 minutes of reaction time to achieve the same pH reduction effect. (Ⅱ) The different forms of calcium content determine the differences in the leaching rate of calcium ions between the two types of fly ash. In CFB fly ash, calcium mainly exists in the form of CaO, and its loose and porous morphological characteristics are more conducive to the leaching of calcium ions. In contrast, in coal-fired power plant fly ash, calcium mainly exists in the form of tricalcium silicate, where the spherical shell in a glassy state limits the release of calcium ions. (Ⅲ) Under conditions of 0.2 MPa and 25 ℃, CFB fly ash can achieve carbon fixation of 39.6 gCO2/kg of fly ash, while pulverized coal furnace fly ash can achieve carbon fixation of 78.2 gCO2/kg of fly ash.