Submarine gullies belong to the submarine micro-geomorphology， which are smaller than the scale of submarine canyons and channels. Submarine gullies are less than 10 km long， less than 1 km wide， and less than 100 m deep. They form deep-water sediment-transport systems with submarine canyons and channels. Owing to the limitation of survey data resolution in previous studies， the important role of submarine gullies has been ignored in the evolution of the continental margin and the process of deep-water deposits. Submarine gullies are the "capillaries" of the deep-water sediment transport system occurring at dozens or even hundreds of times the sum of submarine canyons and channels. Moreover， submarine gullies are mainly distributed in the head of the deep-water sediment transport system， including continental slopes， island-and-reef margins， estuarine alluvial fan fronts， submarine canyons， and channel interiors. Submarine gullies are closely related to the safety of deep-water engineering and islands-and-reefs， process of deep-water deposits， and prediction of deep-water oil and gas reservoirs. The research progress of submarine gullies is introduced from the aspects of identification characteristics， sedimentary environment， influencing factors， and formation mechanisms. From the aspects of distribution area， slope gradients， shape， and sedimentary characteristics， the differences and relationships between submarine gullies， submarine canyons， and channels are discussed， and a method for distinguishing them is given. By summarizing the characteristics of submarine gullies around the world， submarine gullies are defined as linear grooves characterized by erosion or deposition caused by gravity flows in the steep seafloor （slope gradients >2°）， which show the characteristics of submarine gullies as narrow， short， shallow， and straight （curvature≈1）. Moreover， submarine gullies caused by sheet-like turbidity currents have group characteristics that are parallel to each other and equally spaced.