Abstract: This paper introduces a method of recovering ammonium chloride from sodium chloride and ammonium bicarbonate double decomposition mother liquor by phase diagram theory. According to the phase diagram of the NaCl-NH_4Cl-H_2O ternary water-salt system at 25℃ and 60℃, evaporation crystallization and cooling crystallization processes were combined to recover NH_4Cl from the double decomposition mother liquor wastewater, with the recovery process principle and operation parameters being discussed. The purity of NH_4Cl recovered near the co-saturation point of ammonium chloride and sodium chloride is about 95 %, while the purity is more than 95 % when ammonium chloride obtained by cooling crystallization at 25℃.