The accumulation of coal gangue poses significant environmental challenges, necessitating the development of eco-friendly utilization strategies. This study demonstrates that the thermophilic bacterium Bacillus aerius acts synergistically with coal gangue to promote alfalfa growth in sandy soils while improving soil fertility. The combined treatment enhanced plant morphological traits, soil nutrient availability, beneficial microbial communities, and associated biological activities, with these effects supported by molecular evidence. As the first study to verify this growth-promoting mechanism, our findings address a critical knowledge gap and provide a theoretical foundation for the sustainable utilization of coal gangue in the ecological restoration of degraded soils.