Due to the devastating flood occurred in Thailand from July 2011 until the end of year 2011, there are many losses in term of human loss, social loss, and economic loss. Therefore this study concentrates on studying of the flood and looking forward to the future situation under the impact of climate change. This study is to develop the distributed hydrological model, which can reproduce the phenomena of flood in year 2011, and to apply the model for a further study of future flood situation under the impact of climate change in the Chao Praya River basin.