Abstract: Flowable solidified sludge prepared with a composite Flowable soil stabilizer (CFSS) exhibits properties such as high fluidity, self-compaction, and controllable strength; however, its wetting-drying cycle durability has not been thoroughly investigated. In this study, sludge was stabilized using CFSS to investigate the effects of wetting-drying cycles and the CFSS content on the performance of flowable solidified sludge. The microstructural evolution mechanism responsible for its wetting-drying cycle durability is analyzed using XRD and SEM. The results demonstrated that with increasing wetting-drying cycles, the surface deterioration, mass loss rate, and water content of the flowable solidified sludge progressively increase, while its dry density decreases. The UCS initially decreases, follows by a slight increase, then underwent goes a gradual reduction until it eventually stabilizes. With increasing CFSS content, the detrimental effects of wetting-drying cycles on the specimens' appearance are mitigated, mass loss is reduced, and specimens with higher CFSS content exhibit superior mass stability. Furthermore, water content decreases, whereas dry density and UCS increase progressively. A linear correlation is observed between the wetting-drying stability coefficient and the CFSS content. After five wetting-drying cycles, the intensity of the ettringite diffraction peaks decreases, with the crystal morphology transitioning from columnar to acicular, disordered arrangement, and lower distribution density. Concurrently, the number of pores increases, the pore size enlarges, and the compactness decreases. An increase in CFSS content leads to higher ettringite diffraction peak intensity, a reduction in soil micropores, the formation of more hydration products, and consequently, enhances specimen compactness. These microstructural changes provide a coherent explanation for the observed macroscopic behavior. CFSS-stabilized sludge exhibits satisfactory wetting-drying cycle durability, which provides theoretical support for the engineering application of CFSS.