Abstract: This is an article in the field of mining engineering. The deep sand gravel type pore brine in Qaidam Basin belongs to the unsaturated chloride type brine with high calcium, high sodium and low potassium. 480 kg of gravel-type pore brine at 1000～2000 meters underground in Dalangtan mining area was selected for the test, and evaporated and crysta-llized in the natural state in summer. The distribution law of ions in the solid and liquid phases, the salt crystallization law and crystal morphology were analyzed, and the main precipitation characteristics of potassium were studied. The results show when evaporating in the outdoor natural state, the salt precipitation process is mainly divided into four stages: halite→carnallite→bischofite→tachyhydrite. The salt evolution law in the halite stage conforms to the phase diagram of Na⁺, K⁺, Mg²⁺//Cl^-—H₂O at 25 ℃, and that in carnallite and bischofite stages conforms to the phase diagram of K⁺, Ca²⁺, Mg²⁺//Cl^-—H₂O system at 25 ℃. There is a separate precipitation stage of potassium, at which potassium is mainly precipitated in the form of carnallite, and the recovery rate of potassium is 85.76%. The K⁺content in the potassium mixed salt can reach 9.27%, which is a high quality raw material for the production of potassium fertilizer. Calcium precipitates after the brucite stage. The experimental results can provide references for the development and utilization of this type of brine.