The phase equilibria relationship between the quaternary system LiCl-KCl-Li2SO4-K2SO4-H2O and its subsystems LiCl-KCl-H2O and LiCl-Li2SO4-H2O was studied by the isothermal dissolution equilibrium method at 288.15 K, and the corresponding phase diagrams were drawn. At 288.15 K, ternary systems LiCl-KCl-H2O and LiCl-Li2SO4-H2O all belong to the simple type. In the phase diagram of the quaternary system LiCl-KCl-Li2SO4-K2SO4-H2O, there are five equilibrium solid phase crystallization fields: LiCl center dot 2H(2)O, KCl, Li2SO4 center dot H2O, K2SO4, a nd Li2SO4 center dot K2SO4. Compared with the multitemperature phase diagrams of this system at 288.15-348.15 K, it was found that the basic configuration of the phase diagrams is the same. As the temperature increased, the phase region of double salt Li2SO4 center dot K2SO4 clearly increased, whereas the phase region of single salt KCl and K2SO4 clearly decreased. On the basis of the experiment, the extended Harvie-Weare model of the Pitzer model was used to predict the solubility data of the quaternary system. The simulated and measured values were basically in good agreement.