Red mud geopolymer mortars were prepared with thermally activated alumina red mud as main raw material.The effects of the kinds and dosages of chemical activators on the mechanical properties and red mud geopolymer synthesis mechanism were dis cussed.The results showed that sodium silicate,gypsum-alkali with mass ratio of 2∶1 and lime-alkali with mass ratio of 2∶1,can improve the reactivity of alumina red mud and promote the synthesis of red mud geopolymer.Among them,sodium silicate（the amount-of-substance ratio of silicon oxide to sodium oxide is 1.5） had the most remarkable modification effect.The optimum dosage of sodium silicate,gypsum-alkali and lime-alkali was 20%,7% and 10%,respectively.When the dosage of sodium silicate was 20% compressive and flexural strength of red mud geopolymer mortar at 28 d were 32.1 MPa and 6.0 MPa,respectively.The kinds and dosages of activator changed the alkalinity of red mud geopolymer mortar system,adjusted the depolymerization of aluminosilicate and the condensation process of geopolymer,and thus,affected its mechanical properties.