Reverse flotation-cold crystallization process technology is to use the different adsorption capacity of carnallite and sodium chloride on special collectors to separate carnallite from sodium chloride, so that the purity of carnallite raw materials reaches the process allowed Range (NaCl≤7.0%), then add water to decompose carnallite, magnesium chloride enters the liquid phase, control the supersaturation of potassium chloride in the carnallite decomposition system, and achieve the purpose of making potassium chloride particles grow under normal temperature