Silicate cement as a conventional soil curing agent has problems of high energy consumption and high emissions, and researchers have been seeking a more economical and environmentally friendly alternative to cement. In this study, geopolymers based on ground granulated blast-furnace slag (GGBS) and fly ash (FA) were used to reinforce sandy soils, and the effects of different factors on the mechanical properties of geopolymer stabilized sandy soils were investigated by adjusting the type and ratio of exciter, slag-fly ash ratio, water-cement ratio, and curing conditions. The specimens were studied in depth by unconfined compressive strength (UCS) test, electron computed tomography (CT) analysis, and scanning electron microscopy (SEM). The results show that the GGBS-FA-based geopolymer can effectively improve the mechanical properties of the sandy soil; the reinforcement effect of the composite exciter is better than that of the single-component exciter; the low temperature does not significantly reduce the final mechanical properties of the geopolymer stabilized sandy soil, but only delays the polymerization reaction and structure formation; the alkaline environment promotes the strength of the geopolymer stabilized sandy soil; the acidic environment and prolonged exposure to air reduce the strength of geopolymer stabilized sandy soils.