Expansive soil swells with water and shrinks with water loss, causing serious safety problems for construction projects. This study emphasizes alkali-activated binder (NaOH excited fly ash) stabilized expansive soil. We found that swelling decreased with an increase in the amount of NaOH in alkali-activated binder. It was found that the alkali-activated binder stabilized expansive soils (AABS) had higher shear strength than untreated expansive soils (US), manifested by increased cohesion and friction angle. In AABS, the highest cohesion and the highest shear strength were found when the NaOH mass was 6% of the fly ash mass. The strength of AABS was similar to that of US without curing. AABS had higher strength than US after 7 and 14 days of curing. The unconfined compressive strength increased with extension of curing time. Combined with XRD and SEM analysis, it was shown that the mechanism of AABS was the formation of C−S−H and (C,N)−A−S−H and the change in the internal structure of expansive soil. This investigation can solve both the expansive soil problem and provide new concepts for green development.