Abstract: The 3D reconstruction and quantitative characterization of drainage channels and coarse tailings particles in a bed were conducted in this study. The influence of variations in the azimuthal angle (θ) and polar angle (φ) of coarse particles on drainage channel structure was analyzed, and the drainage mechanism of the bed was studied. Results showed that water discharge in the bed reduced the size of pores and throat channels, increasing slurry concentration. The throat channel structure was a key component of the drainage process. The φ and θ of particles changed predominantly along the length direction. The changes in φ had a cumulative plugging effect on the drainage channel and increased the difficulty of water discharge. The rake and rod formed a shear ring in the tailings bed with shear, and the θ distribution of particles changed from disorderly to orderly during the rotation process. The drainage channel was squeezed during the shearing process with the change in θ, which broke the channel structure, encouraged water discharge in the bed, and facilitated a further increase in slurry concentration. The findings of this work are expected to offer theoretical guidance for preparing high-concentration underflow in the tailings thickening process.