Abstract: The freezing crystallization law of the magnesium sulfate subtypes brine at low temperature from Dalangtan Salt Lake in Qinghai province was researched.The salt lake is a typical subtype magnesium sulfate brine lake，and the change of physical properties and the crystallization law of salts during the freezing crystallization at low temperature were also investigated.Results showed that the order of crystallization behavior was：MgSO4·7H2O→MgSO4·6H2O→Na2SO4·3K2SO4 when low freezing brine from 0 ℃ to-16 ℃.Liquid phase composition analysis and solid phase X-ray diffraction analysis showed that the most suitable freezing temperature should be controlled at about-8 ℃.At this point，SO42- mass fraction was lower than 2%，the brine could be simplified as Na+，K+，Mg2+∥Cl—H2O quaternary system and achieved the goal of exploitation of potassium chloride.These data provided a theoretical basis for the comprehensive exploitation and utilization of the brine of Dalangtan Salt Lake.

Key words: magnesium sulfate subtypes brine, deep freezing, crystallization law of salts, phase diagram application