Apparatus and methods are related to treating waste water containing ammonium salts, which contains NH4+, SO42−, Cl−, and Na+. In such a method, the pH value of the waste water to be treated is adjusted to a specific range in advance; sodium sulfate crystal and relatively concentrated ammonia are obtained by first evaporation, and then sodium chloride crystal and relatively dilute ammonia is obtained by second evaporation; alternatively, sodium chloride crystal and relatively concentrated ammonia is obtained by third evaporation, and then sodium sulfate crystal and relatively dilute ammonia are obtained by fourth evaporation. Ammonia, sodium sulfate, and sodium chloride from the waste water are recovered so that the resources in the waste water can be reused.