The stability of loess high-fill slopes is a crucial issue in engineering, where the presence of fissures significantly impacts slope stability. This study investigates the seepage-mechanical response and fissure evolution characteristics of loess high-fill slopes under the coupled effects of consolidation, rainfall, and evaporation through model testing. The disaster chain evolution process of the slope under these coupled effects is revealed. The results show that the development of fissures in loess high-fill slopes does not follow a directional pattern and has a uniform influence on soil properties. Under rainfall, the slope exhibits preferential flow paths, which guide the deformation and failure modes. With the development of fissures, the fill material shows a cumulative damage effect, leading to progressive performance degradation and continuous decline in slope stability. This study enriches the theoretical framework for stability analysis of high-fill fissured slopes and provides guidance for disaster prevention and mitigation in loess regions.