The article analyses the temporal-spatial changes of profiles by EOF (Empirical Orthogonal Function) analy-sis and DTM analysis of GIS. These profiles, which are not affected by engineering, are chosen from the coast with succes-sive field monitoring data from 1990 to 1999. Temporal and spatial EOF indicates the obvious stability of coast profile param-eters in Fengxian tidal flat. In spatial scale, high tidal flats and deep-water terraces are in a balance state while upperclino with steep slopes are sensitive and the stability is easy to be destroyed. In temporal scale, the erosion and deposi-tion in this area are kept in balance in a whole. There are almost no change below -8 - -9.5m. At the same time, it isthe lower limit of tidal affection and the erosion and deposition process from it to high tidal flat keep in balance for manyyears. So the closure depth is appointed to from -8m to -9.5 m (Wusong datum mark).