A temperature-dependent thermodynamic model was developed for representing the solid-aqueous equilibria in the quaternary NaCl + KCl + RbCl + H2O system based on the previous ones for binary and ternary systems. The solid-liquid equilibria in the quaternary system were first predicted by the developed model and then verified by conducting the experiments at T = 298.15 K by an isothermal equilibrium method with equilibration times of 5 and 160 days, respectively. The predicted univariant curve saturated with NaCl(cr) and (K,Rb)Cl(ss) in the system is in good agreement with our experimental data. Moreover, to verify the reliability of the model for the prediction of solid solution composition that coexisted with NaCl(cr), the XRD quantitative analysis technique based on the inverse Vegard approach is used. The experimentally determined solid solution compositions well support the results predicted by the model, indicating that the model can simultaneously predict the compositions of aqueous solution and solid solution that coexisted with a pure salt, i.e., NaCl(cr), in a system under an equilibrium state. Finally, phase diagrams of the quaternary NaCl + KCl + RbCl + H2O system at a temperature range of 273.15-373.15 K were predicted. These diagrams are useful for the future industrial applications.