The solubility variation of the phase system HCl-KCl-H_2O at 25 ℃ is reported when θ_HK(interactions between two species with the same charge) and Ψ_HKCl(interactions among three species) are changed within ±10%. The calculated results indicate that the interactions among the three species are much stronger than that between the two species, whereas the combination of the two kinds of interactions result in great changes of the solubility of the system. This results is important for the salting out technology of the water-salt system.