Abstract: To improve the strength, shrinkage and erosion resistance of backfill material, the research on the optimum mix ratio was studied by modern material modification technology. Using desulphurized gypsum, lime, fly ash, portland cement and tailings sand coarse aggregate as experimental materials to study the influence of the proportion of several admixtures in aggregate on the strength and shrinkage of the specimen by orthogonal tests. The microscopic mechanism of the modification was investigated by scanning electron microscope. The results show that the optimum mixing ratio of the modified filling material is 56% aggregate, 4% fly ash, 10% lime, 10% gypsum and 20% cement. External admixtures have improved the properties of raw soil materials from physical and chemical aspects, and the change of pore structure and the enhancement of particle adhesion are the fundamental reasons for the improvement of strength, shrinkage and water resistance.