Vapor liquid equilibrium (VLE) data are reported for mixed electrolyte solution systems containing NaCl + KCl + H2O, K2SO4 + MgSO4 + H2O and NaCl + CaCl2 + H2O. The measurements were carried out with a pressure between 6.3 and 101.3 kPa in a computer-controlled glass apparatus. A modified NRTL model based on the hypothesis of hydration was used in this paper. Literature data for electrolyte solutions, with temperature spanning from 273.15 to 415.85 K, were successfully correlated using the model. Meanwhile, the model was also successfully applied to predict the VLE data in mixed electrolyte solution systems with the binary parameters.