Abstract: With the increase of population and development of economy in Shanghai, the demand of land increases rapidly, and the contradiction between human and land becomes more and more badly. The population of Shanghai will be 17.5 million, and the demand of land will be 2 267 km\+2 by 2010.The ultimate way is to accelerate reclaiming of tidal flat and landmaking,because Shanghai faces three side waters. How to choose reasonably the borderline of accelerating reclaming tideal flat and making land is an important problem of coastal and estuarine engineers. The depositionerosion change of East Nanhui tidal flat of the Yangtze estuary is rationally simulated by DEM(Digital Elevation Model)and GIS(Geography Information System)technology from 1996 to 1999.By Comparing this method with the traditional method of landform analysis, the synthesis method of DEM and GIS is quickly calculated,with less workload and supernal precision.The research results are as following:the 0.5~1 m elevation zone is the balance zone of erosiondepostition in Nanhi tidal flat,up that zone,the tidal flat is depositional, down that zone,the tidal flat area is eroded. According to the practical instances deepwater river dredge about the Yangtze estuary, and on the basis of the hydrology and suspend sedimentation data of the Yangtze estuary and the land making practice about lower tidal flat,we think that the 0.5~1 m elevation zone is the rational area as borderline about accelerating reclaiming and making land. The research results will provide the theory for the sustaining development of tidal flat resources in Shanghai.

Key words: DEM, tidal flat, erosiondeposition, making land