Abstract: The geological environment of the northern South China Sea is complex and rich in oil and gas resources. It is necessary to examine the physical and mechanical properties of seafloor sediments. Hence, this paper reports a preliminary study of the geological environment. In this study, a series of tests to determine various factors including water content, density, and specific gravity, are conducted in conjunction with miniature vane shear, micro penetration, and compression tests on samples collected in June 2015. The study includes investigating types of seafloor sediments and index parameters of the physical and mechanical properties of soil in the northern South China Sea. The results of the investigation indicate that the surficial seafloor sediment in the study area is mainly composed of silty clay and clayey silt with high moisture content, low density, and low mechanical strength. The variation in the fore-mentioned parameters is generally correlated with the depth of the seabed. Additionally, sedimentary environment, grain size composition, and age are determined as important factors controlling the properties of the sediments to a significant extent.