Biogenic coal-bed methane (CBM), a kind of unconventional gas resources, has been observed in different coal-rank basins. The composition and the diversity of microbial community involved in biogenic CBM have been investigated by metagenomics and high-throughput sequencing. It is fundamental for unravelling the mechanism of biogenic CBM. This review focuses on recent advances in microbial diversity, metabolic pathway, and the function of microbial community in biogenic CBM production. The associations between coal ranks and microbial diversity are further discussed and analyzed.