Ionic liquids (ILs) as green solvents were first proposed to capture low-carbon alcohols (e.g., methanol, ethanol and 1-propanol) from the syngas tail gas. The vapor–liquid equilibrium (VLE) data for the binary mixtures of low-carbon alcohols with 1-ethyl-3-methyl-imidazolium diethyl phosphate ([EMIM][DEP]) were experimentally measured. The UNIFAC-Lei model demonstrated the best performance in predicting VLE data among all the investigated predictive molecular thermodynamic models. However, the COSMO-SAC-UNIFAC model could reproduce the low-carbon alcohols gas absorption characteristics without any experimental data input, and was more accurate than the original UNIFAC and COSMO-SAC models in this case. Using quantum chemistry calculations and wave function analysis, the separation mechanism was revealed on a molecular level. The relationship between thermodynamic behaviors and hydrogen bond interactions in CO₂–low-carbon alcohols–[EMIM][DEP] systems was systematically explored. Additionally, theoretical guidance for the design and screening of task-specific ILs in condensable gas separation processes was provided.