Abstract: The mechanism of application of coal fly ash in water treatment is discussed，and the progress of water treatment，such as dye wastewater，phenol wastewater，heavy metal ions wastewater，removal of ammonium and phosphate，is reviewed. The modification methods of coal fly ash are introduced from acid-modified，alkali-modified，salt-modified，surfactant-modified，mix-modified and synthesizing zeolite. Finally，the future development of coal fly ash is also presented.