This study seeks to clarify the process of development and the change of freight flows in the influence areas of Pyeongtaek and Dangjin Port, which opened lately. The results of analysis are as follows: from development period to growth period, the relation between the development of the port and the change of the hinterland and foreland shows no great change and the freight concentration rates of the first hinterland and foreland decreased, but those of periphery region increased. While the composition rate of import and export freight of vehicle, fuel and energy decreased, the rate of imported freights (iron or steel, other textile articles, rag and organic compounds) and exported freight (manufacture of basic metals) increased. The reasons for such changes in influence areas of port were the increase of export to China and the U.S.A. in the development period, the increase of import from China in the growth period and the diversification of nations from which fuel and energy were imported.