Abstract: The inter-crystal brine in Jianbei lowland of Qinghai Province，where the climate is dry-and-hot in summer and cold in winter，is the typical sulfate-type brine.In order to know the evaporation process of this type brine in natural conditions，took the inter-crystal brine of Jianbei lowland as the research object.At first，evaporated the brine according to the metastable phase diagram of Na⁺，K⁺，Mg²⁺//Cl^-，SO₄^2-－H₂O（15 ℃），then took four groups of brine with different Mg²⁺ during the sodium chloride saturated stage as the freezing experimental samples，and investigated the freezing process in -7 ℃ and -16 ℃ respectively.Results showed the SO₄^2- and Na⁺ separated out in the form of Na₂SO₄·10H₂O，which changed the concentration in liquid phase and made the point of the brine in phase diagram move from the area of picromerite to potassium chloride. Then separated and evaporated respectively，and the results showed that more carnallite could be got by evaporating frozen brine.Therefore，it is significant for the production of KCl using this type brine.

Key words: sulfate-type brine, phase diagram, freezing, evaporation, carnallite