As a municipal solid waste, waste glass undergoes pozzolanic activity when ground to a certain fineness. In this paper, calcium carbide residue (CCR) and Na2CO3were used as composite alkali activators for a glass powder-based composite cementitious system. A total of 60% fly ash (FA) and 40% ground granulated blast furnace slag (GGBS) were used as the reference group of the composite cementitious material system, and the effects of 5%, 10%, 15%, and 20% glass powder (GP) replacing FA on the rheological behavior, mechanical properties, and microstructure of alkali-activated composite cementitious systems were investigated. The results showed that with the increase in GP replacing FA, the fluidity of the alkali-activated materials gradually decreased, the shear stress and the equivalent plastic viscosity both showed an increasing trend, and the paste gradually changed from shear thinning to shear thickening. Compared with the reference sample, the fluidity of the alkali-activated material paste with a 20% GP replacement of FA was reduced by 15.3%, the yield shear stress was increased by 49.6%, and the equivalent plastic viscosity was elevated by 32.1%. For the 28d alkali-activated material pastes, the compressive strength and flexural strength were increased by 13% and 20.3%, respectively. The microstructure analysis showed the substitution of FA by GP promoted the alkali-activated reaction to a certain extent, and more C-A-S-H gel was formed.