The effects of using waste glass as substitution of natural river sand fine aggregate on the mechanical properties and acid resistance of fly ash-slag based geopolymer mortar were investigated. With the aid of X-ray diffraction（XRD）， Fourier-transform infrared spectroscopy（FTIR）， and field emission scanning electron microscopy with energy-dispersive X-ray spectroscopy（FESEM-EDS）， the crystalline phase compositions as well as the reaction process of the paste at the curing age from 1 d until 56 d were analyzed. Besides， the development of interfacial transition zone （ITZ） between paste and aggregates before and after sulfuric acid exposure was highlighted. The results show that both glass and sand slow the geopolymerization reaction rates in the early stages， and the reaction of the sand aggregate mortar is gradually stopped after curing up to 28 d. The compactness increase of glass aggregate mortar at later ages is attributed to the dissolution of the glass aggregate edge in alkaline environment， which increase n（SiO₂）/n（Al₂O₃） for the gel system. The degradation mechanism of the geopolymer mortar in a sulfuric acid environment is found to be based mainly on the destruction of alumina-silicate structure with dealumination， the leaching of metal cations， as well as the micro-expansion microcracks and aggregate falling off due to gypsum crystal growth. However， the glass introduces a better bond with the paste at the ITZ after acid attack， which results in a significantly low compressive strength and mass loss.