Salt effect on the extractive distillation was discussed thoroughly in terms of scaled particle theory. A relationship of salting coefficient and relative volatilities at infinite dilution with salt and no salt was obtained. For the non-polar solute systems DMF/C4 and ACN/C3, we have calculated relative volatilities at infinite dilution with salt which were in agreement with experimental values. But the theory is unsatisfactory for the polar solute systems, glycol/ethanol/water and ethylene glycol/acetone/methanol, because in this case the interactions between polar solutes and solvents are very complicated. The salt effect on the relative volatilities can only be qualitatively analyzed in terms of scaled particle theory for the polar solute systems. But for separating non-polar systems or polar systems by extractive distillation, it is possible to optimize the solvents with salt. A set of experimental apparatus has been set-up to test the effect of adding salts. This work provides a way to optimize the solvents.