Abstract: Magnesium hydroxide was prepared with the analytic-pure magnesium chloride as raw materials，and dolomite lime milk got from the calcination and digestion of dolomite，as the precipitating agent.The products were characterized by the X-ray diffraction（XRD），thermal gravimetric and differential thermal analysis（TG-DTA），and scanning electron microscopy（SEM） etc..The main influencing factors，such as reaction temperature，chloride magnesium concentration，feeding speed，and aging time on the quality of the magnesium hydroxide were investigated.Results showed that under the feed rate of 3 mL/min，aging time of 1.5 h，reaction temperature of 60 ℃，and magnesium chloride concentration of 2.0 mol/L，the effective separation of calcium and magnesium could be realized and high purity magnesium hydroxide products could be obtained.

Key words: magnesium chloride, dolomite, magnesium hydroxide