For the problem of high water demand and high viscosity of geopolymer, the effects of sodium lignosulfonate (SL), polycarboxylate superplasticizer (PC), naphthalene surperplasticizer (N) and melamine superplasticizer (M) on the performance of red mud-fly ash based geopolymer were investigated. The stability of water reducing agents in alkali solution and the effects on the phase, morphology and structure of red mud-fly ash based geopolymer were analyzed by FTIR, XRD and SEM-EDS. The results show that all the four water reducing agents could improve the fluidity of slurry with the same liquid-solid ratio, and the degree of fluidity improvement is N, M, SL, PC in the order from high to low. SL and N have an improved effect on the compressive strength when the dosing is not higher than 0.50% of the dry basis mass, and the effects on the compressive strength are N, SL, M, PC in order from excellent to poor. The addition of water reducing agents does not change the phase composition of geopolymer. SL and N are relatively stable in alkali solution, but PC and M are less stable in alkali solution. The optimum admixtures of SL, PC, N, M are 0.50%, 0.75%, 0.50%, 0.50% (mass fraction), respectively.