Abstract: Abstract: Anaerobic digestion is one of the most effective technologies to valorize biomass waste for bioenergy production. However, complex characteristics of raw materials and varied operating conditions of the reactor resulted in multiple inhibitions during anaerobic digestion. Therefore, improving the performance of anaerobic reactors and reducing the inhibitory effects have attracted increasing attentions. Unlike mediated interspecies electron transfer (MIET) by hydrogen or formic acid, direct interspecies electron transfer (DIET) can directly transfer electrons among microbes. Establishing DIET could enhance the stability of digestion, improve reaction efficiencies, and relieve inhibitory effects during anaerobic digestion. However, DIET is still in its infancy stage. To this end, this study aim to summarize the main mechanisms of interspecific electron transfer, in particular, review and discuss the effects of DIET on relief of inhibitions of anaerobic digestion. DIET can be established via e-pili, OmcS and conductive materials between syntrophic bacteria and methanogens. Compared with electron transfer via MIET, DIET shows several advantages. Electron transfer rate of DIET is 8-9 times that of MIET. In addition, DIET does not depend on the medium to transfer electrons, which indicates that it has no requirement of hydrogenase or formate dehydrogenases, thus avoiding unnecessary energy loss. What's more, during the DIET, electrons are directly transferred between bacteria and methanogens, and it avoids the loss of electrons caused by the diffusion to surrounding environment. Further, the effects of DIET on different inhibitions were summarized and discussed. Present studies indicated the inhibitions caused by nitrogen heterocyclic compounds, aromatic organics and furans, and accumulated volatile fatty acids could be significantly relived with the establishment of DIET. In addition, DIET was also proved could effectively improve the anaerobic digestion with inorganic inhibitors, high content of ammonia and sulfur-containing compounds. Adding conductive materials or ethanol could stimulate the establishment of DIET and enrich DIET related microbes, so as to alleviate the inhibitory effects and strengthen the activities of microbial communities. The enriched DIET related microorganisms were also summarized in this review. So far, microbes included Geobacter metallireducens , Geobacter sulfurreducens,Syntrophus aciditrophicus and Methanothrix harundinacea,Methanosarcina barkeri, Methanosarcina horonobensis,Methanosarcina mazei were confirmed involved in DIET. Other syntrophic bacteria, such as Desulfovibrio, Syntrophus, Syntrophobacter, Pseudomonas, Thauera, Rhodoferax, Clostridium, Syntrophomonas, Veillonella, Streptococcus, Tepidimicrobium, Parabacteroides, Bacteroides, Anaerolinea and Gordonia showed a potential to establish DIET with Methanogens. Lastly, future researches and application prospects of DIET for relieving inhibitions of anaerobic digestion were proposed. 1) The direct evidence for verifying DIET related microbes should be provided. Most of present studies proposed DIET related microorganisms were based on indirect evidence, such as the specific enrichment by conductive materials and improved methane production; 2) It has been speculated that hydrogenotrophic methanogens also participated in DIET. However, MIET will also be promoted in the system dominated by hydrogenotrophic methanogens. The roles of DIET and MIET during anaerobic digestion with inhibitors are desperate to reveal; 3) In depth mechanisms of relieved inhibitions via addition of conductive materials need further exploration. There is an urgent requirement for building up the corresponding relationship between physicochemical properties of additives and establishment of DIET; 4) The techno-economic analyses and environmental evaluations of conductive materials should be conducted to provide insights for commercial application of DIET enhanced anaerobic digestion.