Abstract: Slope instability is one of the most important geohazards to offshore structures.It can cause great damages to oil production platforms,pipelines and electric cables which are based on the seafloor.In this study,a typical sea area in Chengdao Oilfield in the subaqueous delta of the Yellow River is chosen as the study area.Geophysical prospecting and geotechnical drilling are processed to get the stratification and the mechanical characteristics of the soil within the upper 10 m depth.The stability of the slope in this area is calculated using GEO-SLOPE/W.It turns out that slope instability may occur in clayey silt in the surface of the seafloor.The potential failure modes are discussed.It is concluded that the large waves caused by storm tides are the dominating triggering sources.