Abstract: The flame-retardant magnesium hydroxide was synthesized by liquid precipitation reaction method with Xuwen brine as raw material.This process was as follows：A buffer solution of Na2CO3-NaHCO3 was added into the reaction system firstly，and then NaOH was added as the precipitant.The phase and crystal morphology of magnesium hydroxide samples were characterized by X-ray diffraction（XRD） and scanning electron microscop（SEM）.The magnesium hydroxides with a well- defined shape as well as smooth surface could be obtained under the following conditions：concentration of NaOH was 0.4 mol/L，reaction temperature was 75 ℃，and crystallization time was 24 h.The SEM revealed that the magnesium hydroxide form with fine dispersive capability and uniform distribution.The process was not only simple，but also production cost less and environment preserved.Therefore，it had higher potential economic benefits．

Key words: magnesium hydroxide, brine, flame-retardant, buffer solution