The Ariake Sea, a typical closed bay on the west coast of Kyushu Island, has been suffered several external impacts. However, the relative contribution of the various factors and processes of such impacts is still unclear. We have conducted field observations inside an artificial tidal flat to model the physical, chemical and ecological attributes of the tidal flat system in effort to preserve and recover the coastal environment of the Ariake Sea. In this study, the ecosystem and habitat of the artificial tidal flat was investigated by field observation over a 4- year period following the construction in October, 2002. Sediment has deposited in sub-tidal zone due to erosion of inter-tidal zone and inflow from outside the pond by rain and wind. Organic substance in the sediment is in proportion to soil content at sea, although it is dependent on eating by Benthos at inter-tidal zone. To use of the "minimum function" which selected the minimum SI could verify the accuracy of the Habitat Suitability Index model.