Abstract: Aiming at the problem of seepage field of a valley tailings reservoir，based on the measured topographic map of the reservoir and the survey data of rock and soil strata，according to the method of terrain generalization，the terrain generator of MIDAS/GTS software is used to import the actual terrain，and a three-dimensional numerical calculation model reflecting the terrain and geological structure characteristics of the tailings reservoir is established. The GTS seepage analysis module is used to simulate the three-di⁃ mensional seepage field of the tailings reservoir，and the spatial distribution position of the tailings reservoir saturation line is obtained. The results show that the geometric shape of the valley tailings reservoir is controlled by the complex terrain of the valley，the boundary shape is complex，and the distribution of the seepage field is relatively disordered. The results of GTS seepage analysis are in line with the actual law and can be used as a reference for engineering.

Key words: MIDAS/GTS, 3D seepage field, tailings reservoir, line of saturation