When the tailings still do not reach the expected mass fraction under the dewatering process conditions by vertical sand silo or deep cone thickener, the addition of admixture in the tailings is an effective means to achieve secondary rapid dewatering. Taking t the fine copper ore tailings whose bleeding ability was poor, and the mass fraction was still not up to standard after dewatering by the deep cone thickener as the example, the secondary dewatering experiment was carried out with three groups, one adding the A-type admixture another adding the B-type admixture, and the third one without adding admixture. The experimental results show that the bleeding amount of slurry with adding admixture is significantly greater than that without adding admixture after 1 h and 2 h. With the increase of bleeding time, the bleeding amount of slurry with adding admixture and without adding admixture is basically equal at 4 h. Through the regression equation of dewatering mass fraction and dewatering time in three cases, the mathematical model of secondary dewatering of concentrated tailings was obtained, i.e. the relationship between the secondary dewatering mass fraction and the dewatering time is exponential function. Finally, the mechanism of rapid dewatering and structural strengthening of tailings by adding admixture were analyzed. Adding admixture not only increased the mass fraction of tailings, but also improved the stability of tailings, which has potential engineering application value.