The solubility data, composition of the solid solutions, and refractive indices of the LiCl-LiBr-H2O and CaCl2-CaBr2-H2O systems at 288.15 K were studied with the isothermal equilibrium dissolution method. The solubility diagrams and refractive index diagrams of the two systems were plotted at 288.15 K. There is no invariant point, one univariant solubility curve saturated with solid solution, and one crystallization field of the solid solution in the phase diagrams. The two systems belong to the solid solution type, and no double salts formed in the systems. The refractive indices calculated with an empirical equation agree well with the experimental data: By combining the composition equations and solubility equilibrium constant equations of the solid solutions, the solubilities of the two systems at 288.15 K were calculated on the basis of the Pitzer and Harvie-Weare models. The calculated solubilities agree well with the experimental results.