Abstract: The old Yellow River Delta in Jiangsu province has been an abandoned delta since 1855 when the Yellow River changed its course to Shangdong province. With the exhaustion of sedi-ment supply from river,the subaqueous and land part of abandoned Yellow River Delta has being eroded by wave and tidal current. The large scale erosion at submarine delta and the trans-portation of eroded sediment reflects the erosion process. As a result, the coast along this area become the only one part of ?10m isobath near shore most closely in Jiangsu province. In the mean while, under the erosion and sedimentation adjustion in one and a half centuries, the un-ceasing erosion at the area that is deeper than ?10m and ?15m has been restrained effectively and its topography tends to stable. At the region of subaqueous slope that lies between isobath of ?5 m and ?10 m, as the trend of isobath tends gadually parallel to the longitudinal axis direction of tidal current, the profile of subaqueous slope has being adjusted gradually, side-ero-sion on the slope caused by tidal current has being weakened. At the shoal area that is shallower than ?5m, because of the establishment of defense buildings, the severe recess of coastline caused by wave is checked. As a result, the wave-induced erosion on sea bed is confined within the limited area that lies between the stable coastline and subaqueous slope where erosion is de-cline. The adjusting of tidal flat profile can be detected from the recess of curvature on the pro-file and the "down cutting" on the shoal.However, according to macroscopic natural environment, the present evolution of subaque-ous topography is still in the adjusting stage,which is made up with "weakening" and "down cut-ting" of erosion process. Under the action of powerful wave and tidal current, erosion on the shoal that is composed of silt sediment which is widely distributed in local area and subaqueous topography still is the main characteristics of topography evolution. Therefore , the severe move-ment of suspended material and abundant supply of sediment that is generated by erosion will become main impeding factors for local harbor constuction in the future. And then, we must at-tach importance to study engineering measures when making plan for harbor construction, so that can guarantee the progress of harbor engineering construction.

Key words: the old Yellow River, under water delta, stability, seaport building