To understand how extracellular polymer substances (EPS) as additives promotes methanogenesis, batch tests of methane production potential in anaerobic reactors with the addition of EPS or not were conducted. Research showed that EPS increased remarkably methane production during anaerobic digestion (36.5% increase compared with the control). EPS enriched functional microorganisms such as Firmicutes, Actinobacteria, Synergistetes , and Chloroflexi . Among them, 8.86% OTUs from the important hydrolysis and acidification phyla, which may be an important reason for the enhanced methanogenic capacity of anaerobic granular sludge. Additionally, EPS also improved the abundance of cytochrome c (c-Cyts), accelerating the direct interspecies electron transfer (DIET) between syntrophic bacteria and methanogens, thus enhancing the methane production. Interestingly, the average particle size, volatile suspended solids/total suspended solids (VSS/TSS) and EPS content of anaerobic granular sludge (AnGS) in the EPS reactor were approximately equal to that of the control reactor during the anaerobic digestion, illustrating that EPS could not affect the physicochemical properties of AnGS. Therefore, these results suggested that EPS mainly played a role in the form of conductive materials in the anaerobic digestion process. Compared with conductive materials, EPS as biomass conductive materials was not only environmentally friendly and economical but also no secondary pollution.