The developed groundwater pipe network drainage system in the gravel soil slope has a significant impact to its stability. Considering the underground water level monitoring result, this paper simulates the xikengkou slope after the excavation and rainfall conditions based on fluid-solid coupling. The result presents that excavation at toe of slope damaged the groundwater discharge path. In the rainfall condition, the groundwater level increases significantly, which leads displacement occurring within the gravel soil slope. On the other hand, the displacement makes the drainage system be further destroyed and the permeability coefficient continues decreasing. Finally, the high water table leads the slope stability decreasing considerably, even to instability.