Abstract: Rainfall can lead to the degradation of the mechanical properties of loose soil slopes, which poses a substantial threat to the infrastructure and personal safety in the surrounding areas. In order to investigate the degradation laws of the dynamic and static mechanical properties of loose soil under different moisture content conditions as well as the stability performance of slopes, direct shear tests and biaxial friction tests are carried out under various moisture content conditions. The evolutionary patterns of the cohesion and internal friction angle of soil samples at different moisture contents are analyzed. A shear stress difference function is established to analyze the stability of slopes with different slope angles. The results indicate that under different moisture content conditions, there are variations in the strengthening bonding effect and lubrication action of water on the soil mass. When the moisture content is lower than 8.7%, the static shear strength of the soil mass increases as the moisture content rises. Conversely, when the moisture content exceeds 8.7%, the static strength of the soil mass weakens with the increase in moisture content. Moreover, the dynamic friction property of the soil mass exhibits a monotonic decreasing trend with the increase in moisture content. As the moisture content increases, the critical thickness of the overlying soil layer for slope instability gradually decreases, and the degree of influence of mechanical property degradation on the initiation of landslides gradually diminishes. The findings of this study can provide an experimental foundation for the stability analysis and support plan design of loose soil slopes.