Using an isothermal dissolution equilibrium method, solid-liquid equilibria in the quaternary system NaBr KBr Na2SO4 K2SO4 H2O were studied at T= 348 K. The phase diagram, water diagram and the density-composition diagram were plotted according to the experiment results. One double salt Na2SO4 center dot 3K(2)SO(4) was found in the quaternary system at T = 348 K. There are five areas of crystallization, seven univariant solubility curves, and three invariant points. Respectively, the five crystallization regions are Na2SO4 center dot 3K(2)SO(4), NaBr, KBr, Na2SO4 and K2SO4. Based on the chemical model of Pitzer's electrolyte solution theory, the solubilities of the quaternary systems NaCl-KCl Na2SO4 K2SO4 H2O, NaBr KBr-Na2SO4-K2SO4-H2O have been calculated at T = 348 K. The calculation diagrams were plotted. Comparing experimental measurement with calculation, the results showed that the calculated results are in accordance with experiments. (C) 2016 Published by Elsevier B.V.