Based on the characteristics of unclassified tailings in the Sijiaying iron mine, experimental research on exploitation of new backfilling cementing materials that can replace the cement was carried out using lime, desulfurization gypsum, slag, and other solid wastes. Using scanning electron microscopy(SEM)and X-ray diffraction(XRD)analysis, the hydration mechanisms of the new backfilling cementing materials were analyzed, and the optimum ratio of activators was determined. The results show that the strength of the new backfilling cementing materials can meet the filling body strength requirements for safe mining in the Sijiaying iron mine when the mass fractions of slurry, lime, and desulfurization gypsum are 68%, 3. 5%, and 16. 0%, respectively, and the cement-sand ratio is 1∶8. The results also show that the new backfilling cementing materials have a more compact structure and coarser occurrence when compared with the cement. The hydration products of the new backfilling cementing materials are mainly AFt crystals and C-S-H gel, which greatly increases the age strength of the new backfilling cementing materials.