Abstract: In order to explore the feasibility of preparing cemented filling materials with Baixiang‐ shan ultrafine tailings，based on the analysis of the physical and chemical properties of the materials，the strength of the filling body and the fluidity of the filling slurry were tested，and the curing mechanism was analyzed by XRD and SEM.The results show that the whole tailings of Baixiangshan belongs to low-sulfur and low-silicon iron tailings，which are ultra fine tailings with poor gradation. Compared with desulfuriza‐ tion gypsum，the use of anhydrite in the fluid cementitious material significantly improves the strength of the filling body sample at each age. When the concentration of tailings slurry is 55%，the cement-sand ra‐ tio is 1:6，and the flow gelling material is BX6，the compressive strength of the filling body sample at 3，7 and 28 d is 0.55，1.32 and 2.42 MPa，respectively，and the fluidity is 123 mm，which can meet the filling requirements of Baixiangshan Mine. The phase composition and microstructure analysis show that the fill‐ ing body sample is mainly composed of quartz，ettringite and C-A-H gel. The hydration products are inter‐ woven and filled with each other，effectively wrapping the fine particles in the whole tailings，which is ben‐ eficial to improve the density and mechanical properties of the material. Compared with solid cementitious materials such as general cement，the developed fluid cementitious material has the characteristics of high efficiency and low cost，and has good economic and environmental benefits，which can provide data sup‐ port and theoretical guidance for the application of ultra fine total tailings in iron mine filling.

Key words: unclassified tailings, fluid cementitious materials, cemented backfill, compressive strength, flowability, consolidation mechanism