Flood hazard is one of the most harmful disasters in the world for over 40% of the natural hazard damage are caused by flood hazard every year. With the developments of socio-economy, people come to realize that they should not only depend on engineering measures but also use non-structural measures such as flood forecasting, damage evaluation and flood regulation to reduce flood damage. At the same time, along with deepening and broadening of research content on flood control and multi-disciplinary infiltration, people pay increasingly more attention to the studies of multi-disciplinary integrated flood control measures. Meanwhile it is possible to apply computer simulation, remote sensing and GIS technologies to the research field of flood control as well as to the analysis of flood-inundated simulation by GIS on floodplain based on the research of flood prevention and reduction. In southeast China coastal areas there are many size medium or small rivers that flow into the sea separately. Because the flood regulation and storage capacities are low with short flow concentration duration, flood hazard is grave. Besides these basins are situated in the China's developed region, especially in recent years, with rapid growth of economy, enlargement of industrial and city scale, as well as expansion of population, flood losses have also drastically increased. So research on flood hazard prevention and reduction has become an urgency. As floods occur mainly on flood plain in this region, this paper, taking the lower reaches of the Fenghua river in Yongjiang basin of Southeast China as an example, discusses the application of the approaches and methods of remote sensing and GIS to flood-simulation in floodplain. It firstly explores the rainfall runoff characteristics in this basin and floodplain flood routing rules. Supported by remote sensing and GIS the rainfall runoff and two-dimension flood routing models are built, the parameters of models and coefficients of two-dimension numerical calculation models are determined with GIS. Meanwhile the evaluating model of flood submerged area and the damage assessment models are built supported by digital elevation models (DEM) as well as socioeconomic database. Finally a satisfactory calculating result of actual simulated verification is obtained by using remote sensing, telemetering and GIS information. The research indicates that geographic information system and remote sensing create favorable condition for flood-inundated simulation on floodplain. There will be great promise for the application of GIS to the studies of flood prevention and reduction. This research will also provide valuable experience for the flood preventioll and reduction decision-making studies of this region.