In southeast China coastal areas there are many rivers of medium or small size that flow into the sea separately. Because the length of rivers is short and the area of basin is small, their flood regulation and storage capacities are low, duration of flow concentration is short, and therefore flood hazard is grave. Especially in recent years, with rapid expansion in regional economy, losses of flooding have also been drastically increased. Thus, it is significant to develop the research of flood characteristics and prevent flood to reduce calamity. In this paper, taking Chinese southeast coastal Cao-E river catchments as typical case, on basis of the characteristic of flood in medium and small basin, the cause of rainfall runoff and flood routing law are being preliminary to analyses. Flood simulated research of basin have been developed, and rainfall runoff model as well as flood routing model are built. Last the paper emphasis on the approaches and methods that model parameters are derived from the information of remote sensing and GIS are discussed, the calculate precision of models is factory requirement by inspection analysis in experiment catchments. This research will be helpful for the research of rainfall runoff characteristics and flood process simulation. Meanwhile, this research will provide valuable information and a mode for flood simulated forecast with prevent flood to reduce calamity research in the medium and small basin.