Abstract: Open-pit coal mine end slopes are prone to seepage-stress coupling effects under intense rainfall, making their stability a critical concern. Taking the end slope of an open-pit coal mine in Heilongjiang as the research object, a fluid-solid coupling numerical model is established using FLAC^3D to simulate a 24 h infiltration process under three typical rainfall intensities: 20 mm/d, 40 mm/d, and 60 mm/d. The results show that as rainfall intensity increases, the pore water pressure at the slope surface and toe monitoring sections gradually changes from negative to positive, the zero-pore-pressure line moves downward significantly, and the maximum pore pressure at a depth of 0 m rises to 196.1 kPa, indicating intensified deep seepage. The deformation characteristics of the slope exhibit increase settlement and weaken uplift, with the maximum settlement increasing from 0 mm to –24.73 mm, while the original uplift of 42.26 mm gradually disappears. The stability coefficient decreases from 1.695 to 1.385 with increasing rainfall, and the slip surface presents a seated circular shape. Under the 60 mm/d condition, a new slip surface appears for the first time at the first bench. The study indicates that the reduction of matric suction and the rise in pore water pressure caused by heavy rainfall infiltration are the primary mechanisms leading to slope stability degradation and the evolution of the slip surface toward deeper layers. The existing end-slope design can still maintain overall stability under short-term intense rainfall conditions, providing a reference for slope safety evaluation under mine water-control conditions.