Abstract: The three-dimensional topographic map and bathymetric map of the seafloor have been made for the North Nanri Island with the high-resolution multi-beam data. The seafloor topography of the Area A extends from NW to SE characterized by alternative trenches and ridges, while the submarine topography of the Area B is rather flat, and the landform in the middle and northern corner is influenced by islands and reefs. We collect the sediment samples from the study area, and analyze these samples by sieving methods and laser particle size analyzer for grain size distribution. The sediments are divided into 10 varieties according to the Shepard classification. A subsurface sediment distribution map of the study area is made with the data. Grain size parameters, i.e. the mean grain size, sorting coefficient, skewness and kurtosis are calculated, and contour maps are made for each parameter. There have found no geologic hazard factors that would influence the wind power facilities in the study area.