With the development of flame retardant in the world, the nontoxic flame retardant has taken the place of the flame retardant which is toxic and organic. The flame retardant of magnesium hydroxide and aluminium trihydrate are the excellent typical representation of the inorganic flame retardant. Because it has so many excellences,such as good stability, high efficiency, suppressing smog, safety, low price, nontoxic and so on. The flame retardant of magnesium hydroxide and aluminium trihydrate have been got extensive application.