Using the Dongsha offshore radial sand ridges as a study area, the layout design for the offshore sand ridge artificial island was studied under the condition of insufficient basic hydrologic, sediment, and terrain data. With longterm remote sensing data under ebb tide conditions from 1973 to 2014, stability analysis of tidal flats was carried out based on the repetition rate of the exposure area, and the most stable and appropriate dike outlines for sand ridge reclamation were identified based on the distribution characteristics of the repetition rate and the spectral distribution of the grid number. According to the characteristic lines of geomorphological evolution, including the water parting line of the sand ridges and that of the main tide intake subbasin, the internal contours for the water parting lines in the reclamation area and of the main tide intake subbasin were designed.