Abstract: In this paper, four organic acids were used to modified carbide slag via impregnate, and a thermogravimetric analyzer was employed to conduct CO₂ cyclic adsorption/desorption experiments on the carbide slag before and after modification. The physicochemical structure of the modified carbide slag is also characterized to investigate the modification mechanism. The results showed that the Ca in modified carbide slag primarily exists as organic acid calcium and their hydrates, which sequentially transformed into CaCO₃ and CaO upon calcination. The calcination process is accompanied by crystal growth of CaO, with the crystallite size showing jumped increases twice observed at 700 and 800 ℃. The organic acid modification comprehensively reduced the CaO crystallite size, increased the specific surface area of carbide slag, and also weakened the alkaline site strength. The decomposition rate of acetic acid modified carbide slag was as high as 18.2 %/min, which resulting in the smallest average pore size, the richest mesoporous structure, a loose surface morphology and the relatively low crystallite size. Organic acid modification improved the initial CO₂ adsorption capacity of carbide slag, acetic acid modification has the best effect among which, with the carbonation conversion rate of 73.64% in the first cycle and still retained 34.68% after 15 cycles, while formic acid modification showed the worst effect. Specific surface area and alkaline site strength were found to have the greatest influence on the CO₂ adsorption capacity. Therefore, modification of carbide slag should prioritize improving the specific surface area and alkaline site strength, alongside reducing the crystallite size, and increasing the mesopores and micropores content.