The seepage safety and stability of tailings dam is seriously affected by terrain conditions. Reasonable site selection of tailings reservoir is the foundation of safe and stable operation of the dam body in the later stage. Based on the numerical simulation method, the influence of individual topographic factors on the seepage field of dam body is investigated by changing the bank slope, valley width and longitudinal slope ratio of gully and valley. It is found that the slopes of both sides of the valley have the greatest influence on the saturation line of the tailings dam, followed by the bottom width and the longitudinal slope ratio of gully and valley. At the same time, the three-dimensional seepage numerical model of a tailings reservoir is constructed based on the measured digital elevation model (DEM) data of the concrete project and the formation survey data. Subsequently, the topographic factors are extracted to conduct a numerical analysis of the seepage field of the dam body. It is found that the valley topography is the main factor affecting the groundwater flow state, and it is suggested to choose the terrain with relatively small longitudinal slope of gully and relatively flat terrain as the site selection requirements of tailings reservoirs. On this basis, the relationship formula between terrain factors and the elevation of the saturation line established by the multiple linear regression model. The research results can provide a theoretical basis for the safety and stability design of tailings dams.