Microbial electron transfer plays a key role in microbial metabolism and the biogeochemical cycle. The direct contact-dependent microorganism extracellular electron transfer i.e. direct extracellular electron transfer process has become a common focus in different subjects including but not limited to microbiology, geochemistry and biophysics. A series of significant novel findings and theoretical breakthrough in direct extracellular electron transfer have been reported in recent years, such as the molecular explanation of direct extracellular electron transfer, discovery of microbial nanowires and cable bacteria. Along with these new progresses, more problems arise to be addressed, including a more specified direct extracellular electron transfer mechanism in different microbes, effects of direct extracellular electron transfer on the neighbor species and local environment. A cross application of multi-disciplinary theories and technologies is a key to further reveal the process of direct extracellular electron transfer.