Yangla copper mine is going to build a new tailings pond for its tailings disposal. The tailings dam is 185.0 m high and centerline method is used to construct the tailings pond. For the stability of the tailings dam, 2D FLOW program is used for the numerical simulation study about the dam seepage. During simulation calculation, different conditions which include a drainage system installed into the dam or not and different beach widths, i.e. 70 (the flood condition), 100, 300 m (the normal condition), are considered. Through calculation, the change of the seepage under different conditions is obtained, which shows if the drainage system is installed into the tailings dam, the underground water can be successfully drained out. This can keep the phreatic surface level relatively low, so as to improve the stability of the dam.