Under drying-wetting cyclic conditions, the long-term stability of slopes filled by spoil from ditch excavation need special attention. This study focuses on the stability of a spoil slope in Guangdong Province. Laboratory triaxial shear tests were conducted under various numbers of drying-wetting cycles and compaction levels to obtain the shear strength parameters of the spoil under different conditions. Based on the experimental data, a modified strength model integrating drying-wetting cycles and compaction effects was developed, which was then used to study the impact of drying-wetting cycles on the long-term stability of spoil slopes. The study finds that the strength of compacted spoil decreases with the increase of the drying-wetting cycles. For example, with samples at K=0.96 and σ3=20 kPa, the peak strength of the spoil decreased by 21.9%, 33.8%, 40.8%, and 43.1% after 2, 4, 6, and 8 drying-wetting cycles, respectively. Overall, the strength tends to stabilize after 6 to 8 cycles. Although the safety factor of the spoil slope is relatively high in the early stages of embankment construction, it becomes insufficient with increasing drying-wetting cycles. Therefore, it is essential to take a certain safety margin into account in the design of spoil sites, particularly when there are critical facilities downstream. The findings provide valuable insights into the safety margin design of excavated spoil sites.