High-performance aluminosilicate-based cementitious materials were produced with fly ash from a coal power plant as one of the major raw materials. The structures of fly ash containing aluminosilicate-based cementitious materials were compared before and after treatment by the methods of nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM). During the 28 d curing time, the compressive strength of water glass and fly ash samples increased from 9.08 MPa to 26.75 MPa. The results show that most of the stiff shells are destroyed after mechanical grinding and chemical activation. Magic angle spinning (MAS) NMR of ²⁷Al shows that the wide peak becomes narrow and the main peak shifts to the direction of low field, indicating the decrease of polymerization degree, the enhancing of activity, the decrease of six-coordination structure, and the increase of small and symmetrical four-coordination polyhedron structure within the aluminum-oxygen polyhedron network. Comparisons between MAS NMR of ²⁹Si with different treatments suggest that Q⁰ disappears, the quantity of Q² increases, and the quantity of Q⁴ decreases. The polymerization degree of silicon-oxygen is reduced, and the potential activity of fly ash is increased.