The workability of cemented tailings backfill (CTB) is significantly affected by its rheological properties. The influence of fly ash and superplasticizers (SPs) including polycarboxylate (PC), polynaphthalenesulfonate(PNS) and polymelaminesulfonate(PMS) on the rheological properties of CTB mixtures was quantitatively analyzed by using Brookfield RST-SST rheometer in this paper. The results show that regardless of SP type, the addition of superplasticizer will reduce the yield stress and plastic viscosity of CTBs, and the rheological properties are improved with increasing SP dosage. PC is found to be the most effective SP in improving the rheological properties of fresh CTB. However, as hydration time increases, the effect of SPs on the yield stress and plastic viscosity of CTB decreases. With the increase of fly ash content, the yield stress and plastic viscosity of CTBs also show a decreasing trend, due to "morphological effect" of fly ash. The mixture of SP and fly ash has a synergistic effect on the rheological properties of CTB, the modification effect of which is much better compared to that of single mix of SP or fly ash.