Isothermal gas-liquid equilibrium (GLE) data were determined for dilute SO2 in a triethylene glycol (TEG) + water (W) system (TEGW) at 298.15 K and 123.15 kPa, in which SO2 partial pressures were calculated in the range 0-130 Pa. When La3+ was added into TEGWs, GLE data suggested that adding of La3+ ion markedly increased the solubility of dilute SO2. By fitting of these data, Henry's law constants (HLC) were obtained. For acquiring the important absorption mechanism, UV, FTIR, H-1 NMR, and fluorescence spectra in absorption processes of SO2 were investigated. On the basis of these spectral results, the possibility of intermolecular hydrogen bond formation by hydroxyl oxygen atoms in the TEG molecule with hydrogen atoms in the H2O molecule and S center dot center dot center dot O interaction formation by hydroxyl oxygen atoms in the TEG molecule with the sulfur atom in the SO2 molecule was discussed.