Abstract: The hydration mechanism of slag-fly ash excited by sodium metasilicate was studied. The microstructural analysis explained the changes in the microstructure and hydration products of the cementitious materials at different alkali equivalents. The results show that the incorporation of sodium metasilicate can increase the strength of the cementitious material and increase the C-S-H content in the slurry. In addition, the incorporation of 8% sodium metasilicate can increase the hydration product, the internal structure of the slurry is more dense, and the microcracks inside the slurry are reduced.