[Objective] To address the need for improving the mechanical properties and water stability of silt subgrade, this study takes silt stabilized with alkali-activated rice husk ash (RHA) geopolymer as study object and investigates its reinforcement mechanisms and engineering applicability, aiming to determine the optimal combination of activator concentration and RHA dosage.[Methods] NaOH solution and RHA were used synergistically to stabilize silt. Mix proportions were optimized through compaction tests, and macro-mechanical properties were evaluated via unconfined compressive strength tests and disintegration tests. X-ray diffraction (XRD) was used to analyze the composition of hydration products, and scanning electron microscopy (SEM) was employed to characterize the microstructural evolution, systematically revealing the “activation-cementation-strengthening” mechanism.[Results] The results showed that micron-sized RHA particles effectively filled the pores of the silt, while NaOH activated RHA to generate silicate gels, leading to a denser spatial network structure. Mechanical properties were significantly improved: at a NaOH concentration of 10% and an RHA dosage of 7.5%, the unconfined compressive strength reached 1.501 times that of the control group, and disintegration resistance was remarkably enhanced. The micro-macro performance indicated that the interfacial bonding strength of cementitious products is the main controlling factor for the improvements of compressive strength and disintegration resistance.[Conclusion] The alkali-activated RHA geopolymer achieves coordinated improvement of the mechanical properties and water stability of silt through the combined effects of physical filling and chemical cementation. The optimal mix proportion (10% NaOH+7.5% RHA) provides a low-carbon solution for silt subgrade reinforcement and promotes the resource utilization of solid waste (RHA), demonstrating notable engineering, economic, and environmental benefits.