[Objective] The effects of climate change on the stability of organic carbon were revealed from the perspective of the molecular structure of organic carbon in order to provide a theoretical basis for clarifying the impact of future climate change on organic carbon stability and soil fertility in mollisols.[Methods] A long-term field experiment dealing with the simulation of climate change through the use of open-top chambers (OTCs) at the Hailun Agroecological Experiment Station of the Chinese Academy of Sciences provided data for this study. We analyzed the organic carbon content and infrared spectral characteristics of various aggregates and density fractions in the 0-20 cm topsoil of black soil under three treatments:① ambient temperature and CO₂ concentration (aTaCO₂); ② temperature elevated by 2℃ and ambient CO₂ concentration (eTaCO₂); ③ temperature elevated by 2℃ and CO₂ enrichment to (700±25) μmol/mol (eTeCO₂).[Results] Neither eTaCO₂ nor eTeCO₂ significantly affected organic carbon content of the bulk soil compared with aTaCO₂ (p>0.05). However, eTaCO₂ increased soil organic carbon (SOC) contents by 13.45% and 52.89% in the <0.053 mm size aggregates and occluded light fraction (OF), respectively, (p<0.05). eTeCO₂ increased SOC content by 46.89% in the free light fraction (LF) (p<0.05). Compared with aTaCO₂, both eTaCO₂ and eTeCO₂ treatments significantly influenced the SOC molecular structure of the bulk soil. The relative intensity of other functional groups was significantly affected, except for the aliphatic group (p<0.05). Moreover, eTeCO₂ weakened the aliphatic group of organic carbon in the bulk soil and the >0.25 mm size aggregate, but increased the -CH/C=C ratio of organic carbon in the 0.25-0.053 mm size aggregates (p<0.05). Alcohols, aliphatic, aromatic, and polysaccharides were the major functional groups affected by climate change. Furthermore, compared with aTaCO₂, eTaCO₂ and eTeCO₂ increased the -CH/C=C ratio in the LF and OF fractions, accelerating lipolysis in light fractions of organic carbon.[Conclusion] Climate change had no effect on the content of organic carbon in mollisols. Although increased temperature and CO₂ had different effects on the composition and proportion of organic carbon molecular structure, organic carbon storage remained stable in mollisols. Climate change may have little effect on soil organic carbon storage, and the fertility level of the black soil can still be maintained.