Abstract: The submarine fan reservoirs on the northern slope of the Lingshui Depresion of the Qiongdongnan Basin in the western South China Sea consist of fine clastic sediments with poor physical properties, and the occurrance of sweet reservoirs remains unclear. In order to clarify the sedimentary characteristics of submarine fans, this paper takes both the outcrop stratification and lithological association as the guidance, combine the wavelet division frequency interpretation of seismic sedimentology together with the isochronous slicing technique along layers to form the three-dimensional isochronous stratigraphic slice consisting of “point”, “line”, “plane” and “body”. Longitudinal wave impedance, as an effective lithological indicator, are integrated with lithology to form a three-dimensional isochronous depositional system of submarine fans. The study suggests that there are three major waterways formed by strong current, in which filled by the sediments with high sorting and good reservoir properties, while on the flank sides and front edges, such as the overflow natural levee, crevasse fan, and leading edge crevasse, reservoir properties are usually poor due to weak hydrodynamics and poor sorting. It has been confirmed by drilling that the reservoirs on the northern slope of the Lingshui Depression have rapid changes in lithology, and the accurate description of three-dimensional isochronous sandbody is critically important.