With MgCl_2·6H_2O and NH_3·H_2O as raw materials,C_2H_5OH and Twee-80 as dispersing agent,the magnesium hydroxide is prepared by homogeneous precipitation method.Nanometer magnesium oxide was obtained by water wash、alcohol wash、dring and calcination.The results indicate that the optimum technological conditions are as follows: their molar ratio of reactants is(MgCl_2·6H_2O∶(NH_3·H_2O))=1∶2,temperature of reactants is 45 ℃,time of the reaction is 40 min,aging time 2 h,the calcination temperature 900 ℃ and th...