Abstract: The high-sulfur bauxite was preroasted in rotary tube furnace and muffle furnace to investigate the effect of roasting temperature on the settling performance of red mud digested from roasted high-sulfur bauxite. The changes in apparent morphology and phase composition were analyzed and discussed by SEM and XRD, as well as the changing mechanism of the settling performance of red mud. Experimental results indicated that preroasting process makes the apparent morphology of red mud looser and more porous and enables the geothite in bauxite ore to transform into hematite to improve the settling performance of red mud. The overloosened ore after roasting will cause the red mud to be excessively fine, thus making the settling performance of red mud poor to a great extent. Comparing the digested sludge from the preroasted ore in muffle furnace to the digested sludge from that in rotary tube furnace, the latter has better settling performance.