Abstract: The poor flowability of high-concentration tailings slurry often leads to slurry hardening and rake blockages in thickeners. To address this, the study employed computed tomography and rheological measurement techniques to investigate the effect of slurry concentration on static yield stress (τ_B), and a comparative analysis was conducted between thickened tailings and freshly mixed slurry. Results show that the concentration, coarse particle content, and pore structure of thickened tailings are nonhomogeneous. Slurry concentration and the proportion of coarse particles (75–300 μm) increase with decreasing slurry height, while pores in the 50–250-μm range serve as the primary storage space for water. The τ_B of thickened tailings is 5.3–61.3 times higher than that of freshly mixed slurry. Furthermore, τ_B decreases with decreasing coefficient of variation (CV) of slurry porosity. It is proposed to use CV to quantify differences in τ_B between thickened tailings and freshly mixed slurry. Field application at an iron ore mine in China validated the results, providing insights to mitigate slurry hardening in silos.