This paper is based on the extraction of alumina from coal fly-ash, using the raw material of coal fly ash and ammonium sulfate additives, which are calcined and then the easy leaching aluminum ammonium sulfate is formed. The results show that Al2O3 in the coal fly ash released in the form of aluminum ammonium sulfate through adding ammonium sulfate; While n(Al2O3) : n([NH4]2SO4)=1:6, mullite phase of the coal fly ash decomposed completely; but the roasting time is longer than 1.5 h, and the corresponding calcined product phase is mainly aluminum ammonium sulfate.