Abstract: In order to understand the cementitious characteristics of Bayer process red mud from Guangxi Pingguo aluminum corporation，XRD,FTIR,TG-DSC and SEM techniques were used to investigate the hydration products and microstructure of the hardened pastes，which formed after a hydration process of the red mud compound-activated by carbide slag and flue gas desulfurization gypsum.The results indicated that the red mud could show hydraulic cementitious properties after compound-activated by carbide slag and flue gas desulfurization gypsum，and its compressive strength was all higher than 4 MPa at the curing age of 3，7 and 28 d.Ettringite，C-S-H gel，Na-rich meionite，thenardite and aluminum hydroxide were generated in the process of this hydration reaction system.Ettringite crystal overlapped each other to form the skeleton structure，which ensured the strength of cementing materials.C-S-H gel and etc，cemented or filled in the middle of the skeleton structure of ettringite，which reinforced and compacted the structure of the hardened paste.The research results can praide theory reference for application of Bayer Process red mold in underground mining cementitias filling material.

Key words: Bayer process red mud, Hydraulic cementitious properties, Compound-activated, Hydration