With regard to the problems in the decision making of flood retention zones, Mengwa Flood Retention Zone is selected as the case study zone of “Application of decision support system of flood detention zone based on controllable risk techniques”. By integrating multi-source data and models based on GIS techniques and platform, the decision support tools for watershed planning and management of flood detention zones are established to help solve several problems, such as rapid and accurate evaluation of flood losses, efficient and rapid forecasting and alert of flood risks, control and management as well as emergency management framework.