Red mud was stabilized by using（NaOH+Na₂SiO₃）solution， carbide slag and fly ash. Alkali-activated red mud-fly ash-carbide slag composite was prepared. The strength formation and development mechanism of the composite were analyzed by mechanical and microscopic property tests. The safety of the composite was evaluated by heavy metals leaching test. The results show that the strength of the composite increases with the decrease of red mud content and the increase of curing age. The composite containing 40% red mud reaches a maximum compression strength value of 20.1 MPa at the curing age of 28 d. The formation of dense calcium silicate hydrate（C-S-H） and calcium aluminate hydrate（C-A-H）， and the physical combination of red mud particles are the main reasons for the increase in strength. The heavy metals in red mud formed compounds and are solidified in the composite after curing for 28 d. No heavy metals are detected in the leachate after immersion for 28 d， which proved the safety of stabilizing red mud with strong alkali activator， carbide slag and fly ash.