Abstract: Compatibility and processing flow-ability of magnesium hydroxide superfine powder with organic high polymers materials would be significantly improved after being surface modified.Rare earth coupling agent and Wt-200S were chosen as compound modifier for magnesium hydroxide by wet-modification method. <DIV>Surface properties of magnesium hydroxide were measured by surface analysis technique.Initial thermal decomposition onset temperature of modified magnesium hydroxide was measured by DTA and the existence of magnesium hydroxide′s surface modification layer was verified by fourier transform infrared spectroscopy (FT-IS).Meantime,optimum processing condition of surface modification was also studied.The optimal conditions for rare earth coupling agent and Wt-200S as the compound modifiers for magnesium hydroxide as following:mass concentration fraction of sizing agent was 30%,mass ratio of rare earth coupling agent to Wt-200S was 1.9∶1,dosage of modifiers was 2.5%,modification temperature was 80 ℃,stirring speed was&nbsp; 760 r/min,and for modification was 30 min.Under such conditions for modified magnesium hydroxide,oil absorbability was lowered from 0.499 7 g/g &nbsp;to 0.336 5 g/g,activate index was increased from 0 to 99.86%,and initial thermal decomposition temperature was increased from 344.1 ℃ to 366.5 ℃.</DIV>