Abstract: After the analysis about the theory and data of Na⁺，K⁺，Mg²⁺//Cl^-，SO₄^2--H₂O quinary system phase diagram，a new method to deal with picromerite and kainite，the two potassium double salts was put forward.Picromerite and kainite were treated under high temperature condition（100 ℃），then carnallite can be separated out by cooling under low temperature （15 ℃），and by the way of decomposing，potassium chloride can be obtained from carnallite.Under 75 ℃ of high temperature transformation and 25 ℃ of low temperature cooling，the mixed potassium salt in autumn brine from Chabocuo salt lake（sodium sulfate subtype） was studied.Results showed that the potassium conversion rate of the whole transformation process can reach about 80%，which proves the feasibility of the process route.

Key words: mixed potassium salt, high-low temperature, carnallite