To investigate the impact of flood discharge-induced atomized rainfall on the safety and stability of accumulation slopes in dry-hot valley regions, a fully coupled model of flood discharge-induced atomization, surface runoff and seepage of complex slope was established based on the water-air two-phase flow theory. The Eulerian two-fluid model was adopted to describe the motion of water and air during flood discharge, and the coupling relationship between slope seepage and surface runoff was explicitly considered, enabling the numerical solution of the water-air flow process. The results show that the developed coupled model transforms the flux boundary between seepage and runoff into an internal boundary of the model, thereby overcoming the computational challenges caused by inaccurate boundary condition specification. For accumulation slopes, atomized rainfall primarily forms surface runoff, which is characterized by short formation time, high runoff volume, and rapid dissipation. When the influence of surface runoff on slope seepage is taken into account, the rainwater infiltration depth and volume within the slope body generally exhibit an increasing trend.