The pH value, electrical conductivity, density of quaternary ammonium ionic liquids and ethanol solution for absorbing SO_2were researched. The results show that with an increase of temperature, the values of pH decrease, conductivity increase and then decrease slightly, and density decreases. With the increasing concentration of ionic liquids, the values of pH increase and then kept balance, the values of conductivity increase and then decrease slightly, and the values of density decrease. The values of pH and moisture content decrease, electrical conductivity and density increase in saturated solution compared with the former solution, and the system of the saturated CPL-TBAB ILs and ethanol solution are miscible.