Abstract: In order to provide fundamental data for the industrial design of the supercritical fluid extraction, the solubility of benzoic acid was measured in supercritical carbon dioxide without and with cosolvents at the mole fraction of 0.02(ethyl acetate, ethanol or ethyl acetate plus ethanol (molar ratio 1:1)), at the temperature of 35.0, 45.0, 55.0 degrees centigrade and under pressure from 8.0 to 23.0 Mpa, by using a flow-type phase equilibrium apparatus. This article analyzed the influence of temperature and pressure on solubility, the effects of the cosolvents and the mechanism, and then correlated the measuring results with a modified Chrastil equation and a chemical association model respectively. The average relative deviation between calculated values and test results was 7.56% and 4.83% respectively.