Abstract: In order to reveal the high efficiency, timeliness and sustainability of alfalfa (Medicago sativa) on soil improvement in extremely harsh mining environment, the soil microbial community structure and soil nutrient accumulation characteristics of alfalfa land with different restoration years (3, 6, 10 and 15 years) in Yanshan mining area were studied by using high-throughput sequencing technology. The results showed that alfalfa could effectively improve the concentration of nutrients such as soil available nitrogen, available potassium, organic matter and the relative abundance of some dominant microbial groups, including Proteobacteria, Acidobacteria, Ascomycota, Basidiomycota, Sphingomonadaceae, Burkholderiaceae, Rhizobiaceae, Bacillaceae, Chaetomiaceae and Entolomataceae. The effect of alfalfa on soil nutrient improvement was the best in the 6th year. The relative abundance of dominant soil microbial groups increased significantly in the 6th or 10th year, and the restoration rate of bacteria by alfalfa was faster, while that of fungi was slower.