The equilibrium solubility of the quaternary system Na+, NH4+//SO42-, NO3- H2O at 303.15 and 323.15 K was determined by an isothermal dissolution equilibrium method. The weighing bottle method and Abbe refractometer were adopted to measure the density and refractive index of the aqueous liquid phase. The solid-phase invariant points at equilibrium were confirmed by Xray diffractometry. The complete diagrams of equilibrium phase, water content vs J(NO3-)(2) of this quaternary system at 303.15 and 323.15 K were constructed based on experimental data. The phase diagrams demonstrated that the system was a complicated quaternary system at 303.15 and 323.15 K Five single-salt crystallization zones and four double-salt crystallization zones were found in this system at 303.15 K Four single-salt crystallization zones and four double-salt crystallization zones were found in this system at 323.15 K.