Abstract: Changing the surface behaviors of magnesium hydroxide and improving the solid-liquid separation performances of the colloidal magnesium hydroxide slurry are the key techniques in industrially producing high-purity superfine magnesium hydroxide. In order to design the key equipment—solid-liquid separator in the wet modification process of superfine magnesium hydroxide，the existence form of superfine magnesium hydroxide to be modified was assumed，and the floatation and sinking conditions of the modified aggregates were analyzed.On the basis of establishing the floating model，the basic design theory of floating solid-liquid separator for modification of superfine magnesium hydroxide was put forward.

Key words: superfine magnesium hydroxide, surface modification, solid-liquid separator