<p>Debris flow deposits are widespread geological bodies in areas with high seismic intensity. The static and dynamic characteristics of debris flow deposits have become increasingly complex due to periodic heavy rainfall events and earthquakes. This study investigated the degradation of debris flow deposits under wet‒dry cycles through laboratory-based static, dynamic, and SEM microscopic tests. The results revealed a significant decrease in the unconfined compressive strength (UCS) with increasing number of wet‒dry cycles, with a 17.48% reduction after five cycles. The cycles lead to fine particle loss, increased pore size, and altered particle contact forms, reducing overall stability. Cohesion decreases notably with each cycle, whereas the internal friction angle slightly increases, as observed in triaxial tests. SEM analysis revealed that the main mechanism of cohesion degradation was the loss of viscous particles and the evolution of the pore structure caused by wet‒dry cycles. The interlocking effect between particle rearrangement and angular particles gradually strengthens, leading to an increase in the internal friction angle. In addition, the results of the dynamic triaxial tests revealed that as the number of loading cycles increased, the accumulated axial strain gradually increased, especially during the initial loading cycles. Moreover, the damping ratio increases. The dynamic stress ratio, confining pressure, and axial plastic strain are positively correlated. This study links environmental cycling to debris flow sediment degradation, revealing both macroscopic and microscopic mechanisms. It provides essential parameters for evaluating sediment stability in high-rainfall areas, offering a solid foundation for disaster prevention, engineering design, and risk mitigation.</p>