Abstract: The structure of fly ash was analyzed to extend its scope of application. The compressive strengths of Na₂SiO₃ and fly ash blocks modified by four methods were compared to display the chemical reaction speed of fly ash. SEM photographs showed that after mechanical grinding and alkali activation most of the stiff shells of fly ash were destroyed, and MAS NMR of ²⁷Al showed that wide peaks became narrow. MAS NMR of ²⁹Si indicated that Q⁰ disappeared, the quantity of Q² increased but that of Q₄ decreased. It is concluded that after mechanical grinding and alkali activation, the hard shells of fly ash are destroyed, the polymerization degree of silicon-oxygen and aluminum-oxygen is reduced, and the potential activity of fly ash is enhanced.