Abstract: Temperature effect on solid-supereritical phase equilibrium and its molecular basis is studied in this Paper,based on the experimental isobaric solubility data of naphthalene/CO2 binary system.The Gibbs-Konowalow rule as well as PR-EOS are used to calculate the primary factor-solute excess partial molar enthalpy along the isobars.It is found that solute excess Partial molar enthalpy diverge negatively in retrograde region of the system and the temperature effect is significant.The strong exothermicity is explained by using Kirkwood-Buff solution theory.Solute excess partial molar enthalpy is proved to be proportional to cluster size of solvent molecules around a solute molecule.Theory and calculating results show that for an attractive system the stronger negative divergence of solute excess partial molar enthalpy corresponds to the larger cluster size.