Based on the Patterson-Delmas theory of corresponding state and the equation of state by Flory, the polymer-solvent interaction parameter chi(1) in the Flory-Huggins theory has been calculated over a temperature range including the supercritical fluid region of solvent and a wide range of pressure up to 1.0 x 10(4) bar. The temperature dependence of chi(1) parameter at constant pressure over the supercritical fluid region is expressed by a parabolic-like with a maximum, and a closed-loop phase diagram is calculated in nonpolar polymer solution by the Flory-Huggins theory and the temperature dependence of chi(1) parameter in this work.