Caffeine is small molecule with strong polarity (Mejri and others 2009).However,supercritical CO2 is nonpolar,the solubility of caffeine in supercritical CO2 is very low(Wang and others 2004).The involvement of water molecules makes the whole systems more complicated.There are strong interactions among water,caffeine,and supercritical CO2. Caffeine partly dissolved in cold water and completely dissolves in 70C water.Water and caffeine can be combined easily by hydrogen bonds,and the supercritical CO2 can be dissolved in water to a large number