Abstract：To investigate the effect of pulp concentration on the spiral separation process of coarse coal slime, separation experiments were conducted to evaluate the separation characteristics under varying pulp concentra-tions. Furthermore, comprehensive analyses of the concentration effect were carried out by examining the spatial distribution characteristics of flowing film and the migration behavior of multi-component tracer particles at dif-ferent concentrations.The separation tests indicated that, under a constant feed flow rate, increasing the pulp con-centration resulted in a continuous increase in clean coal yield, whereas the ash content initially fluctuated and subsequently increased, indicating that the performance of spiral separation for coarse coal slime first improved and then declined. With an increase in pulp concentration, the distribution width of high-density particles (+2.0 g/cm3) near the inner edge of the spiral channel increased, while the proportion of low-density particles (-1.5 g/cm3) at the outer edge initially rose and then decreased. Medium-density particles (1.5~2.0 g/cm3) exhibited a notable tendency to migrate outward.Flow field measurements revealed that, with increasing feed concentration, the thickness and longitudinal flow velocity of the slurry film at the outer edge of the spiral channel decreased, while those at the inner edge slightly increased. However, the overall distribution still exhibited thicker film lay-ers and higher velocities at the outer edge.Particle tracing experiments demonstrated that finer high-density parti-cles experienced more significant misplacement at the outer edge of the spiral channel, whereas coarser low-density particles exhibited more pronounced misplacement at the inner edge.