Abstract: The ecological restoration of engineering waste slag dumps is of great significance for protecting the surrounding ecological environment and facilitating green construction. Polyacrylamide (PAM) was utilized as a soil structure adjuster, and biochar and river sediment were employed as nutrient modifiers to restore the degraded soil on a waste slag dump in the Central Yunnan Water Diversion Project. Blank control CK, T1 (with PAM application), T2 (with PAM and biochar application), T3 (with PAM and river sediment application), and T4 (with PAM, biochar, and river sediment application) were established to explore the effects of composite material amendment on soil physicochemical properties, plant (Bermuda grass) growth and soil bacterial community structure. The findings indicated that the four treatments could notably enhance soil electrical conductivity, nutrient content, soil mean weight diameter (MWD), and the content of ≥0.25mm aggregates (WR_0.25), and significantly reduce soil bulk density and pH values. Among them, the T4 treatment demonstrated the most superior comprehensive improvement efficiency. The four treatments increased plant height, biomass and mean root diameter, and the T4 treatment showed the best efficacy. The amendment of ameliorants significantly enhanced the relative abundance of the dominant bacteria Actinobacteria and Nocardia, while decreasing the relative abundance of Gemmatimonadota, Acidobacteria, Ramibacer, Massilia, and Sphingomonas. LEfSe analysis showed that the treatments changed the species of marker bacteria in the soil, and the number of specific bacteria in the T2 treatment group was the highest. Correlation analysis showed that the relative abundance of dominant bacteria such as Brevundimonas, Nocardioides and Pseudarthrobacter was positively correlated with plant growth indicators, suggesting that these bacterial genera might play an important role in promoting the plant growth. Redundancy analysis indicated that the MWD, total organic carbon and conductivity were the principal environmental factors regulating the soil bacterial community structure and plant growth, and the indicator parameters for soil improvement in the slag dump. In conclusion, T4 treatment exhibited the best performance in improving soil structure and properties, promoting plant growth and regulating soil microbial community.