Abstract: The stability of deeply excavated expansive soil slopes during the operational period is influenced by multiple factors, including groundwater level fluctuations, inherent fissures, and wetting-drying cycles. However, the deformation and failure mechanisms arising from the coupled effects of these factors remain unclear. To address this issue, a scaled-down physical model of an expansive soil slope incorporating inherent fissures and capable of simulating groundwater level fluctuations is constructed. The model has a geometric similarity ratio of 1:10 and a slope ratio of 1:2.5. The model box is 330 cm in length, 100 cm in width, and 150 cm in height, with a slope filling height of 50 cm. Four wetting-drying cycles and one long-duration rainfall event are simulated, during which groundwater level variations are controlled, and the development of surface fissures as well as internal and external deformations is systematically monitored. The results indicate that: (1) surface fissures exhibit spatially differentiated evolution with fissure ratio and average fissure width at the slope crest progressively increasing with successive cycles, whereas those at the mid-slope and slope toe decrease under the combined effects of groundwater and lateral confinement; (2) inherent fissures exert a dominant control on slope deformation, with the maximum surface settlement on the fissured side at mid-slope reaching 37 mm, and pronounced deformation also occurring in deep soil layers along the fissure plane, while deformation on the non-fissured side is mainly confined to shallow soil within a depth of less than 10 cm; (3) during the fourth drying stage under elevated groundwater conditions, the fissure-seepage coupling effect between fissures and seepage induces a rapid increase in deformation, triggering erosion gullies, toe heave, and shallow slope failures. Inherent fissures not only provide preferential seepage channels for groundwater but, together with groundwater level fluctuations, significantly weaken the soil structure and amplify deformation responses. This study elucidates the coupled evolution mechanisms of fissures, seepage and deformation under the combined action of the groundwater seepage field, the water content field induced by wetting-drying cycles, and the slope mechanical response field, providing theoretical insights and practical guidance for the stability assessment and protective reinforcement design of expansive soil slopes.