This work presents a thermodynamic method for treating nonequilibrium solvation. By imposing an extra electric field onto the nonequilibrium solvation system, a virtual constrained equilibrium state is prepared. In this way, the free energy difference between the real nonequilibrium state and the constrained equilibrium one is simply the potential energy of the nonequilibrium polarization in the extra electronic field, according to thermodynamics. Further, new expressions of nonequilibrium solvation energy and solvent reorganization energy have been formulated. Analysis shows that the present formulations will give a value of reorganization energy about one half of the traditional Marcus theory in polar solvents, thus the explanation on why the traditional theory tends to overestimate this quantity has been found out. For the purpose of numerical determination of solvent reorganization energy, we have modified Gamess program on the basis of dielectric polarizable continuum model. Applying the procedure to the well-investigated intramolecular electron transfer in biphenyl-androstane-naphthyl and biphenyl-androstane-phenanthryl systems, the numerical results of solvent reorganization energy have been found to be in good agreement with the experimental fittings. nonequilibrium solvation, constrained equilibrium, solvent reorganization energy, numerical evaluation Reorganization energy is one of the crucial quantities in the control of electron transfer (ET) kinetics in solution [1][2][3] . It consists of two parts: solvent reorganization energy λ s and inner reorganization energy λ in . Based on Marcus's formulation of nonequilibrium free energy and polarizable continuum model (PCM), several numerical programs have been implemented for evaluating λ s , but this quantity in some cases is theoretically overestimated when compared with those evaluated from experimental fittings [4][5][6] . The most remarkable discrepancy is the predictions towards Closs-Miller experiments [7][8][9][10] .In the well-known Closs-Miller experiments, the ET rates from biphenyl to various acceptors were measured. From the plots of ET rate constants versus driving force, Closs and Miller obtained estimation of λ s and λ in , 59.82 kJ/mol (0.62 eV) and 55.96 kJ/mol (0.58 eV) respectively [7,8,10] . Here λ s is considerably smaller than the calculated results by the analytical model and the numerical solution based on the traditional treatment with continuum model [9,11] . Attempts were made for the improvement on the poor computational results within the framework of continuum model, but it seems that no essential change can be made [12] . In this work, we will firstly present our new theory on this topic and show how we achieve the correct expression of the solvent reorganization energy in virtue of the classical thermodynamics. Relying on the new formulations, we realize the numerical evaluation for solvent reorganization energy on the basis of Gamess package [13,14] . Finally, as an application, we calculate the solvent reorganization ener...