Abstract: Technological conditions of preparing ammonium carnallite with bischfite from salt lake brine after extracting potassium as well as ammonium chloride solution by-produced in the production of magnesia as raw materials were studied.When amount-of-substance ratio of MgCl<SUB>2</SUB> to NH<SUB>4</SUB>Cl was 1∶1,pH=6.0,reaction temperature was at 85 ℃,stirring speed was&nbsp; 500 r/min,heating time was 1 h and crystallization at 7 ℃ for 4 h,crystal ratio of ammonium carnallite after filtration and drying was about 60% at first time.Crystal ratio was over 80% for the second time.Solubility of ammonium carnallite in water was measured at different temperatures.Crystallization kinetic equations were established with kinetic parameters and solubility data at 10 ℃ and 20 ℃,respectively.Kinetic equations proved that the crystallization of ammonium carnallite at low temperature was under the control of mononuclear crystal growth.