In sulfuric acid medium, triisooctylamine was used as extractant to separate perrhenate from the aqueous phase. Molalites of perrhenate in the aqueous phase were measured from 278.15 K to 303.15 K at impurity ionic strength from 0.2 to 2.0 mol.kg(-1). Standard extraction equilibrium constants K at different temperatures were calculated by polynomial approximation method. Some microcosmic property values in the process were investigated and obtained by Pitzer's theory, which indicated enthalpy and entropy were both dominant thermodynamic factors.