Land-cover change has long been recognized as having marked effect on the amount of soil organic carbon (SOC). However, the microbially-mediated processes and mechanisms on SOC are still unclear. In this study, the soil samples in a degenerative succession from alpine meadow to alpine steppe meadow in the Qinghai-Tibetan Plateau were analyzed using high-throughput technologies, including Illumina sequencing and GeoChip functional gene arrays. The soil microbial community structure and diversity were significantly (P < 0.05) different between alpine meadow and alpine steppe meadow, the microbial ɑ-diversity in alpine steppe meadow was significantly (P < 0.01) higher than in alpine meadow. Molecular ecological network analysis indicated that the microbial community structure in alpine steppe meadow was more complex and tighter than in the alpine meadow. The relative abundance of soil microbial labile carbon degradation genes (e.g., pectin and hemicellulose) was significantly higher in alpine steppe meadow than in alpine meadow, but the relative abundance of soil recalcitrant carbon degradation genes (e.g. chitin and lignin) showed the opposite tendency. The Biolog Ecoplate experiment showed that microbially-mediated soil carbon utilization was more active in alpine steppe meadow than in alpine meadow. Consequently, more soil labile carbon might be decomposed in alpine steppe meadow than in alpine meadow. Therefore, the degenerative succession of alpine meadow because of climate change or anthropogenic activities would most likely decreased SOC and nutrients medicated by changing soil microbial community structure and their functional potentials for carbon decomposition.