The process of selective precipitation of Mg²⁺ from multicomponent chloride salt mixed system（0.6 mol MgCl₂+1.1 mol LiCl+3.2 mol NaCl） was preliminarily studied with Na₂CO₃ as precipitate agent.The results indicated that at 25~80 ℃ and the amount-of-substance ratio of total C and total Mg[n（C_T）/n（Mg_T）] was 0.8~1.1,the MgCO₃·3H₂O needle-like particles formed at 25 ℃ and the irregular spherical agglomerates composed of sheet-like Mg₅（CO₃）₄（OH）₂·4H₂O were obtained above 40 ℃.The precipitates formed at 40~50 ℃ were comparatively difficult to be separated by filtration due to the relative dispersion and the small particle sizes.The precipitation ratio of Mg²⁺ was the lowest at 40 ℃.The higher the temperature,the easier the formation of Li₂CO₃ and the higher the ratio of Li⁺ precipitation.The increase of n（C_T）/n（Mg_T） promoted both the precipitation of Mg ²⁺ and Li⁺.At room temperature（25 ℃） and n（C_T）/n（Mg_T）=1.0,the precipitation ratio of Mg ²⁺ was above 98% and the precipitation ratio of Li⁺ was less than 0.1%,the separation effect of Mg²⁺ and Li⁺ was the best.