<p>In mountainous regions with deep and narrow valleys, landslides frequently obstruct rivers, leading to the formation of landslide dams. The sudden failure of these dams poses severe threats to downstream lives and property. Among various engineering measures to mitigate these risks, spillway excavation is one of the most widely adopted strategies. This study conducted flume model experiments to systematically investigate the overtopping failure of landslide dams under different spillway configurations, including variations in longitudinal slope, axis orientation, and downstream surface extension. The analysis focused on breaching discharge, flow velocity, breach evolution, and the morphology of the downstream deposition zone. The breaching process was divided into three distinct stages: overflow erosion, rapid erosion, and attenuation equilibrium. The results indicated that increasing the spillway slope significantly reduced the peak discharge, while changes in axis orientation and downstream extension of the spillway increased the peak discharge and delayed its occurrence. Additionally, both peak flow velocity and the length of the downstream deposition zone exhibited an inverse correlation with increasing spillway slope. Conversely, modifications in axis orientation and spillway extension led to higher peak flow velocities and a reduction in the length of the deposition zone. Notably, breach width evolution was only marginally affected by spillway slope but was closely related to spillway axis orientation. This study provides valuable insights into optimizing emergency spillway design and contributes to mitigating the risks associated with landslide dam failures, offering practical guidance for flood control and disaster prevention.</p>