Abstract: Fineness, water demand ratio, chemical composition and mineral structure of coal fly ashes were measured in this paper. The mechanism of fly ash used in cement, concrete and waste water treatment is expounded. The modification methods of coal fly ash are introduced from mechanical grinding, fire modification, acid modification, alkali modification,surface active agent modification and mixed modification which can improve the quality of fly ash and broaden its utilization way

Key words: fly ash, physical and chemical properties, modification, adsorption performance