Abstract: The present invention relates to the waste water treatment field, and discloses apparatus and method for treating waste water containing ammonium salts, which contains NH4+, SO42?, Cl?, and Na+. In the method of the present invention, 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. The method of the present invention can recover ammonia, sodium sulfate, and sodium chloride from the waste water respectively, so that the resources in the waste water can be reused as far as possible.