Abstract: Two fly ashes were sampled from Wuhai Wuyun power plant and Hohhot Huyi power plant,respectively.Dissolution characteristics of Si and Al from these fly ash samples at hydrothermal synthesis circumstance were studied,and then they were used as a guide to adjust the SiO2/Al2O3 molar ratio of gel system,as a result A-zeolite and X-zeolite were synthesized directionally by hydrothermal synthesis method.X-ray diffraction （XRD） was used to identify the type of zeolite.Effect of alkalinity on the synthesis of zeolite was investigated.The results show that the amount of Si and Al dissolved from fly ash are much less than that in the chemical composition of fly ash;with the increase of dissolution time,amount of dissolved Si increases,while amount of dissolved Al rises first and drops later.Higher alkalinity is beneficial to the formation and growth of A-zeolite crystal nucleus.Besides,X-zeolite also can be synthesized directionally.It could be concluded that it is the Si and Al dissolved from fly ash at hydrothermal circumstance that are available components in the hydrothermal synthesis of zeolite,under guide of which a variety of zeolites can be synthesized directionally.