In salt-rich soft soil regions, as a backfill material, foamed lightweight soil (FLS) is often subjected to long-term chemical erosion of groundwater, which would lead to a continuous degradation of strength properties, and ultimately causes a risk to the long-term safety of infrastructures. Combining sulfate chemical soaking test and dry-wet cycle test, this paper investigates the durability changes of FLS under different densities of FLS, sulfate concentrations, and cation types of sulfate. The results indicate that the dynamic strength degradation of FLS under dry-wet cycles is much greater than that under sulfate soaking. When other influencing factors remain unchanged, the corrosiveness of Na2SO4 solution is greater than that of MgSO4 solution. Moreover, this paper establishes a dynamic strength degradation prediction model for FLS based on the experimental results, which can scientifically guide the durability changes of FLS under different influencing factors.