Interactions between hydroxyalkyl ammonium ionic liquids (HyAA ILs) and sulfur dioxide (SO2) were investigated by quantum chemical calculations using first-principles density functional theory. The optimized geometry, charge distribution, and thermodynamic parameters were obtained and used to identify the effective groups in the ILs that absorb SO2. HyAA ILs react with SO2 and form S—N bonds with an average distance of 0.240 nm. This reaction results in charge transfer from ILs to SO2 as well as changes in the S—O bond length and the O—S—O bond angle. The calculated results from the gas and liquid state models indicate that the standard Gibbs free energy change (△G Θ) of the absorption reaction is mainly determined by the geometry of these cations and their molecular weight. The cation structure influences the energy barrier of the absorption reaction and the activation energy (Ea) changes as follows: Ea(secondary)<Ea(tertiary)<Ea(primary). The theoretical results were evaluated against experimental data and the molar fraction values of SO2 for the primary ammonium IL-SO2 system are in od agreement with the experimental results. This work provides an effective method for predicting and verifying the properties of functionalized ILs.