Abstract: In view of the safety risks such as the failure of flood discharge facilities and the instability of dam body，it is of great significance to check the flood control capacity of flood discharge system and cal⁃ culate the stability of dam body to ensure the safe operation of tailings reservoir. Taking a Fifth-class tailings reservoir in southern China as an engineering example，aiming at the existing problems of limited storage ca⁃ pacity and steep slope ratio of the reservoir，combined with on-site reconnaissance，survey data and similar engineering experience，the study on the change of auxiliary dam body and existing flood discharge system is carried out，and the reconstruction scheme of clearing and filling of auxiliary dam，new construction of in⁃ clined channel-turning-well-pipe flood discharge system and dismantling and plugging of old flood dis⁃ charge system is put forward. The Lizheng software is used to calculate the anti-sliding stability of the auxil⁃ iary dam，and the water balance method is used to check the 100-year return period flood regulation calcula⁃ tion of the new flood discharge system. The results show that the safety factors of anti-sliding stability under normal operation and flood operation conditions of the changed auxiliary dam are 1.84 and 1.79 respective⁃ ly，which are higher than the minimum safety factor limit of the specification. After 100 years of flood regula⁃tion calculation，the highest flood level in the reservoir area is 44.96 m，and the minimum safety supereleva⁃ tion is 0.84 m. The flood control capacity of the new inclined channel-flow well-culvert pipe drainage sys⁃ tem meets the flood fortification requirements of the Fifth-class reservoir. The transformation scheme can ef⁃ fectively improve the safety conditions of tailings reservoir operation，and can provide reference for similar tailings reservoir hidden danger control and safety improvement projects.

Key words: tailings reservoir, flood drainage system, stability of dam body