Anaerobic sludge digestion is a methanogenic process, in which sludge microbiome mediate degradation of macromolecules in waste sludge to generate biogas. In contrast to traditional anaerobic digestion, the influent sludge predominantly consist of microbial cells and their extracellular polymeric substances (EPS), which are persist and resistant to biodegradation. Also, it is a challenge to identify the sources of living microorganisms in anaerobic sludge digesters from influent waste sludge or indigenous digestion populations. Therefore, the population composition, function and their interactions of anaerobic sludge digestion microbiome have rarely been illustrated before. Nonetheless, the rapid development of high throughput sequencing techniques and bioinformatics analytical methods have enable the investigation of microbiomes of complex microbial systems, including the anaerobic sludge digesters. Here, we have comprehensively reviewed and discussed the recent development of anaerobic sludge digestion microbiome in four aspects, with a focus on waste activated sludge: (1) structure and composition of waste activated sludge, and anaerobic sludge digestion; (2) 16S rRNA gene-based analysis methods to study digestion sludge microbiome; (3) metagenome- and metatranscriptome-based analysis methods to study digestion sludge microbiome; (4) case study on digestion sludge microbiome. In addition, major challenges and further developments toward understanding the digestion sludge microbiome are identified and discussed.