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Backfilling mining is thought to play a significant role in controlling the deformation of coal and rock strata and the distribution of underground pressure. This study presents a numerical investigation of the influence of the strength of backfilling materials (BMS) on the deformation of coal and rock strata consisting of multiple goaf during excavation using the backfill mining method. In this study, a numerical three-dimensional fast Lagrangian analysis of continua (FLAC 3D) model was constructed to explore the relationship among the BMS, the displacement of coal and rock strata, and the distribution of underground pressure based on the geological conditions of a mining panel of the Hengda coal mine in the City of Fuxin, China. The numerical results suggest that as the BMS increase, the supporting ability of backfilling materials in goaf becomes stronger. At the same time, when the displacement of coal and rock strata decrease, the pressure on the surrounding rocks decreases and the pressure on the overlying stratum increases. However, the effect of BMS on the coal and rock strata has a limit. When the BMS equals and/or exceeds that of coal, the influence is not obvious. In addition, the displacement and underground pressure in the surrounding goaf are also affected, but in a relatively gentle way. Moreover, during the process of mining, as the BMS increases, the scope and arch area of the underground pressure in front of working face decrease instead. The higher the BMS is, the more stable the main key stratum is. The ability to resist compressional deformation of backfilling materials plays an important role in controlling the displacement of roof and relieving the underground pressure on the overlying stratum. Thereby, the roof stability in front of the working face is helpful for safety in the production of coal mines. Full article