To investigate the microscale dispersion properties of CO2 in polar organic solvents with equivalent alkyl chain lengths, the volume expansion coefficients and solubilities of CO2 in 2-hexanone, hexanal, and 1-hexanol were measured at 318 K under different pressures. A modified Fourier-transform infrared spectroscopy technique was applied in situ to study the microcosmic mechanisms of volume expansion in the three mixtures, from ambient pressure to the supercritical state of CO2 at 318 K. The results show that CO2 and 2-hexanone/hexanal form 2-hexanone-CO2 and hexanal-CO2 aggregations, respectively, with increasing CO2 pressure; the dispersion state of CO2 molecules in the solvent is the primary factor causing the volume increase of the mixture and CO2 solubility. During this process, the original microstructure of the liquid 2-hexanone and hexanal can be broken, and it becomes easier for CO2 molecules to dissolve in the 2-hexanone and hexanal solvents.