The influence of vitreous content on the pozzolanic activity of fly ash is very important. In this study, low-calcium fly ash with vitreous content of 60%, 70%, 80%, and 90% (mass fraction) was selected using the XRD-Rietveld method. The influence of fly ash with different vitreous content on the micro and macro properties of cement-based materials with similar fineness was analyzed and compared, and the hydration activity of fly ash with varying vitreous content was evaluated. The results indicate that, under the premise of essentially consistent fineness, fly ash vitreous content has approximately posititve linear relationship with activity index. Fly ash with 90% vitreous content achieves an activity index of 85.1%, which is 14.6% higher than fly ash with 60% vitreous content. The most significant growth trend of activity index is observed in the fly ash with range of 70% to 80% vitreous content. The increase of vitreous content of fly ash accelerates the hydration process of composite cement at all ages and optimizes the microstructure of cement. In the later stages of composite cement hydration, fly ash with higher vitreous content significantly improves both the mechanical properties and pore structure. After 28 d, composite cement containing fly ash with 90% vitreous content shows a 7.7 MPa increase in compressive strength compared to cement with fly ash containing 60% vitreous content.