The solidliquid equilibria data of the aqueous SrCl2NH4ClMgCl2H2O quaternary system at T = 298 K were measured. Results show that there are three three-salt cosaturation invariant points and five crystallization regions corresponding to one single salt ammonium chloride (NH4Cl), three hydrate salts bischofite (MgCl2 center dot 6H(2)O), strontium chloride hexahydrate (SrCl2 center dot 6H(2)O), strontium chloride dihydrate (SrCl2 center dot 2H(2)O), one double-salt ammonium carnallite (NH4Cl center dot MgCl2 center dot 6H(2)O), and seven univariant curves in the phase diagram. The sizes of the crystalline regions of the salts are in the order of NH4Cl > SrCl2 center dot 6H(2)O > NH4Cl center dot MgCl2 center dot 6H(2)O > SrCl2 center dot 2H(2)O > MgCl2 center dot 6H(2)O. The solubilities of system SrCl2NH4ClMgCl2H2O at 298 K were calculated based on the Pitzer ion interaction model and its extended HarvieWeare model. It can be seen from the comparison of experimental and calculation diagrams that the predictive solubilities agree well with the experimental values.