Abstract:C-S-H and other gelling products are the main source of the mechanical properties of the gelling material, the gelling products are mainly composed of calcium, silicon and aluminum elements, the proportion of calcium and silicon elements directly affect the composition and structure of the gelling products. In this paper, desulfurization gypsum, fly ash and blast furnace mineral powder are used as the main raw materials to prepare ternary composite cementitious materials, and investigate the effects of different Ca/Si (0.9-1.3) on the mechanical properties of desulfurization gypsum-fly ash-blast furnace mineral powder ternary cementitious materials, And then the hydration mechanism of different Ca/Si cementitious materials was tested and analyzed by using microstructural characterization such as XRD, SEM, EDS, FTIR and TG, Based on the experimental results, its main conclusions are as follows: Under the condition that the optimal Ca/Si is 1.1, the compressive strength reaches 62.2 MPa after 28 days of curing when using SiO2/Na2O of 1, water glass dosage of 10%, and water-cementitious ratio of 0.5, and the leaching concentration of As, Pb, Cd, Cr, Ni, and Zn in the cementitious material is in line with the national Ⅳ class of environmental quality standards for surface water; Suitable Ca/Si can fully promote the hydration reaction of internal calcium, silicon and aluminum elements, which can improve the setting time and flow degree to a certain extent, and give enough time to promote the full reaction of silicate, aluminosilicate and calcium to generate sufficient amount of cementitious products to improve the material density.