Abstract: In order to explore the activation mechanism of different activators on fly ash,fly ash from combustion and gasification industries was roasted and activated by mixing with sodium carbonate,calcium carbonate,ammonium sulfate and concentrated sulfuric acid,respectively.The changes of minerals after calcination and activation were analyzed by XRD. The results show that the aluminum in combustion ash is mainly in the form of mullite,while the gasification ash is mainly in diopside form.The sodium carbonate tendes to form nepheline after calcination and activation,and its optimum activation temperature is 1 000 ℃.Calcium carbonate is calcined to form calcium feldspar,and the optimum activation temperature is 1 300 ℃.Ammonium sulfate tendes to form aluminum ammonium sulfate,and its optimum activation temperature is 500 ℃.Aluminum ammonium sulfate could be decomposed into aluminum sulfate at 550 ℃; and ammonium sulfate activates to produce sulfuric acid and nitrogen containing gases.The aluminum sulfate is the predominant product after sulphuric acid calcination and activation,and the optimum activation temperature is 400 ℃.Calcium in gasification ash is easily to form anhydrite during activation,and this increases the amount of ammonium sulfate and sulfuric acid.The activation temperature of those four activators is in order of calcium carbonate> sodium carbonate > ammonium sulfate > concentrated sulfuric acid. Therefore,the concentrated sulfuric acid activation method with low activation temperature is more promising.