Microbial electrolysis anaerobic digestion (ME-AD) systems employs microbial electrochemical technology to stabilize and stimulate methane production of conventional anaerobic digestion, while the mechanism remains obscure. This project intended to figure out the microbial community composition and the key functional genes in ME-ADs under different electrode potential. Then a mechanism of ME-AD was inferred based on these results and so as to identify the optimal potential and production. DNA were extracted from 9 systems with both the biofilm (with one system excepted) and suspension collected, in total 17 samples. Shot-gun sequencing were used to generate the metagenomic libraries and then metagenome assembly genomes (MAGs) were generated by binning.