The calculation of anti-slip stability is an important part of the safety evaluation of tailings pond. Since it is not possible to effectively estimate the excess pore water pressure caused by the rise of the tailings pond, the total stress method is often used for stability analysis. However, there may be excess pore water pressure in the whole life cycle of the tailings pond, and the influence of this part of the excess pore water pressure cannot be ignored. Based on Biot's consolidation theory, a flat tailings pond is taken as an example, and the finite element method is used to qualitatively analyze the generation and dissipation of excess pore water pressure in the section of tailings pond during dam-filling and decommissioning, and then the stability calculation of the effective stress method is carried out. The results show that: 1) The excess pore water pressure reaches the maximum at the end of the dam-filling, which is about 130 kPa, and it takes about 28 a for it to dissipate completely; 2) At the end of dam-filling, the safety factor of anti-sliding stability calculated by effective stress method is 1.486, and with the increase of effective stress of dam body, the safety factor after excess pore water pressure is completely dissipated reaches 1.648, with an increase of about 11%; 3) The effective stress method can be used to consider the influence of excess pore water pressure on the stability of the dam body during the rising process of the tailings pond in detail, and the results are more scientific and reliable.