Chianan Coastal Plain had been built since late Pleistocene. It was marked by the lagoons and offshore bars. The coast has been changed coincidently with transgression and regression. Since last three hundred years, it has prograded westward due to rapid sedimentation. Lagoons of Benkang, Wangkang and Taofeng have been filled up and reclaimed as fish ponds or salt pans. However ,the west coast of offshore bars, Haishan and Wangyeh, have been eroded with a maximum rate of 12m/yr in average. In addition, the offshore bar migrated landwardly, such as the northern section of Waishanting bar moved toward the land with a rate of 58 m/yr during 1904-1990. Responding to the abundant sand supply from Choshui River, the sand dunes distributed in Peikang coastal plain are wider than those in Chiayi. They scattered on the coast plain below 7m and could be built after Tahu transgress (3500-4000 yr B. P.). They lie in four bands approximately, which might indicate four different stages of coastline. Most of the sand dunes decreased in altitude caused by humans modification in 1990 comparing with 1904 and 1926, which become cemetery field in landuse. Overall, bi-directional relationship existed between human and landform in the coastal plain since last three hundred years. The coastal changes produced some impact on human beings including the decline of small sea ports, changes of landuse and threat of flood. In contrast, the human activities influenced the geomorphological change such as reclamation of tidal flat, construction of dike and reservoir, etc.