Abstract: To effectively separate and extract lithium from deep brine, the phase equilibria of the ternary system LiCl + CaCl₂ + H₂O was determined by isothermal dissolution method at 348.2 K. The composition and density of the equilibrium liquid phase were determined. The equilibrium solid phase composition was determined by Schreinemakers wet residue method and X−ray diffraction method. It is found that at 348.2 K, the ternary system belongs to simple type system without the formation of double salts, and the phase diagram is composed of one invariant point, two univariate curves and two crystallization phase regions (CaCl₂·2H₂O, LiCl·H₂O), which belongs to the hydrate type I phase diagram. By comparing the phase diagram of the ternary system at 273.2 K, 283.2 K, 298.2 K, 323.2 K and 348.2 K, it can be found that: CaCl₂·6H₂O, CaCl₂·4H₂O, LiCl·CaCl₂·5H₂O and LiCl·2H₂O exist in the system at 273.2 K and 283.2 K, and the crystallization phase region of the double salt LiCl·CaCl₂·5H₂O increases with the temperature increasing, while the crystallization phase regions of the single salts CaCl₂·6H₂O, CaCl₂·4H₂O and LiCl·2H₂O all decrease. When the temperature changes from 283.2 K to 298.2 K, the crystallization phase regions of LiCl·CaCl₂·5H₂O and CaCl₂·4H₂O increase and the crystallization phase region of CaCl₂·6H₂O decreases, meanwhile the crystalline phase of lithium chloride changes from LiCl·2H₂O to LiCl·H₂O. When the temperature changes from 298.2 K to 323.2 K, the crystalline form of calcium chloride changes from CaCl₂·6H₂O and CaCl₂·4H₂O to CaCl₂·2H₂O, and the double salt LiCl·CaCl₂·5H₂O disappears. When the temperature changes from 323.2 K to 348.2 K, the crystallization phase region of CaCl₂·2H₂O increases and that of LiCl·H₂O decreases. The results show that the interaction between lithium and calcium ions is simple and there is only single salt crystal at higher temperature, which is conducive to the separation and extraction of lithium from the chloride type brine coexistence with lithium and calcium.