Soil organic matter (SOM) strongly influences microbial-driven nutrient cycling; however, its role in shaping bacterial carbon metabolism in reclaimed mining soils remains underexplored. We established a greenhouse pot experiment simulating SOM accumulation during restoration, with five SOM levels (1.1%-3.5%), to assess impacts on bacterial diversity, abundance, and carbon metabolic activity using molecular and biochemical assays. Results showed that SOM significantly increased bacterial diversity and metabolic function, with peak diversity at 2.5% SOM. High SOM content was associated with increased abundance of carbon metabolism-related genes and biofilm-forming bacteria. Structural equation modeling revealed that SOM directly enhanced microbial diversity and indirectly stimulated carbon metabolism by altering soil pH and nutrient status. These findings highlight SOM as a central ecological driver of microbial carbon cycling and support SOM-enrichment strategies for restoring soil microbial functions in degraded mining environments.