Abstract: The tailings from the Yinshan Mine contain approximately 51% ultrafine particles of less than 19 μm, presenting significant challenges to the thickening and dewatering processes. In particular, the effectiveness of deep cone thickeners is particularly affected by seasonal variations and the quality and concentration of the tailings feed. In order to improve the settlement performance of the deep cone thickener at the Yinshan Mine. Comprehensive experiments were conducted, including physical and chemical property tests, laboratory−scale flocculation settlement experiments, and semi−industrial experimental focusing on the flocculation of ultrafine unclassified tailings. The results showed that DR1030 proved to be the optimal flocculant. At a tailings slurry concentration of 10%, the consumption of DR1030 was 30.0 g/t in summer and 33.0 g/t in other seasons; at a 15% slurry concentration, the consumption was 35.0 g/t in summer and 38.0 g/t in other seasons. Under semi−industrial experimental conditions, the actual consumption of DR1030 was 34.0 g/t, which was 4.4 g/t less than that of the existing flocculants. Furthermore, the underflow concentration with DR1030 exhibited more stable and higher mass concentration, which was improved by 2.6%. Slump flow measurement demonstrated that DR1030 had no significant effect on the fluidity of the slurry. This study provides critical process parameters that can improve cemented paste backfill quality at the Yinshan Mine, as well as valuable insights for similar mining operations.