Abstract: The sludge height and underflow rate are the two most important parameters for deep cone thickeners. Therefore, studying the law of change of the underflow concentration with sludge height is important. Discontinuous or continuous dynamic compaction processes of the tailings were investigated physically by using a small, self-made deep cone thickener. Using the power function relation between effective void ratio and mud pressure and combining with force analyses of the tailing particles, this study deduced a mathematical model of underflow concentration and sludge height. The results revealed the inner floc structure relation between underflow concentration and sludge height of the deep cone thickener. In addition, the law of change of this model was explained by applying a spatial structure theory of tailings particles. Based on the requirements for the underflow concentration of mine production, the mathematical model was applied, the reasonable range of sludge height was presented, and the reliability of this model was verified. Moreover, this mathematical model provides a theoretical basis for the design and operation of deep-cone thickeners.