We have developed a prediction method that can express such a system thermodynamically based on the solvation model. The solvation model can express the salt effect fully in terms of change of liquid phase composition and total vapor pressure. In our model, we assume that: 1.Both volatile components make solvates with each ion of a salt. 2.The salt is perfectly ionized to anion and cation. 3.Solvates cannot contribute to vapor liquid equilibria. 4.A free volatile component can contribute to the equilibria. 5.The free volatile component is not affected by the solvate. 6.The activity coefficient is divided into two parts: •expression of non-ideality •vapor pressure lowering Thus, the number of liquid molecules that determine vapor-liquid equilibria changes from that in the original composition. We call this resulting changed composition the “effective liquid composition”. Using these assumptions, our model affords a more versatile method for predicting and correlating VLE for electrolyte solutions.