Abstract: The Southern Yellow Sea is identified as advantaged sea area for evaluation of nonprofit and strategic offshore oil and gas resources in China. Currently, the study on the sedimentary characteristics and geotechnical properties in the depth direction of seafloor sediment in the sea area is sparse. By measuring and analyzing the particle size and physical-mechanical properties of the sediment cores collected from 287 stations in June 2009 and June 2010,we obtain the spatial characteristics and geotechnical properties of seafloor sediment in the west-central area of southern Yellow Sea. Investigation indicates that the types of surficial seafloor sediment in the study area are very diverse. The surficial seafloor sediments in the southwest study area, where the sediments are easily scoured and become coarser due to strong hydrodynamic conditions, are mainly composed of silty sand and sandy silt with high mechanical strength and low compressibility. The surficial seafloor sediments in the northeast study area consist mostly of silty clay and clayey silt with low mechanical strength and high compressibility. Sediments are not uniform in the seafloor, and often composed of a few types of sediments interbedded. The variation of fundamental physical properties and mechanical properties of the sediment with depth is mainly related to sediment types, and secondly compaction. To a certain extent, the fitting function proposed in this study can be used to estimate the porosity of seafloor sediment in the study area if the compressional wave velocity is known.