In this paper we have systematically studied V-L equilibrium in ternary aqueous solutions containing volatile weak electrolytes by introducing a ternary interaction term into Edwards generalized molecular thermodynamic model and optimizing several adjustable parameters. The program PARA9 with flexible functions of doing a series of calculations has been developed and carried out on a TQ-16 computer. It can be used either for direct calculation of V-L equilibrium or optimizing the adjustable parameters. For the systems (NH3-CO2-H2O

NH3-H2S-H2O and NH3-SO2-H2O) satisfactory results have been obtained with relative mean deviation of 5-10%. Besides

several sets of adjustable parameters and valuable information of activity coefficients and equilibrium concentrations of ions and molecules in solutions are obtained.