Abstract: Longitudinal gravity flow deposits, as a kind of important deep-water reservoir, are critical to the exploration of natural gas in the Yinggehai Basin for the time being. Based on the integrated drilling, logging, seismic and regional geological data, the depositional characteristics and evolutionary history of the Miocene longitudinal gravity flow in the Basin is studied by the authors. Discussed are also the hydrocarbon accumulation conditions and controlling factors of the lithologic reservoirs of gravity flow. Facts show that the Miocene reservoir is a kind of thick massive fine sandstones favorably deposited in some distributary channels and lobes in deep water. In the time of Miocene, a great amount of sediments was supplied by the Hainan uplift and surrounding fault slope breaks. They filled the longitudinal depressions as gravity flow deposits with favorable forming conditions of lithologic reservoirs characterized by great thickness, large area and proximity to source rocks. Structural fissures are well developed. Therefore, excellent trap conditions are available in the area and they should be the future exploration targets in the Yinggehai Basin.