The basic concept and systematic structure of interactive flood forecasting system has been introduced in this paper. Some main key techniques of interactive forecasting such as sub-basin topological linking, operation table, parameters optimizing and interactive modification has been analyzed. As an example, the system component, data flow of real time operational flood forecasting and application results of Huaihe River interactive flood forecasting system has been described. Based on the analysis of geographic and flood characteristics in China, this paper points out the necessity for building interactive flood forecasting system in China as while as the main issues which should pay attention to in the development of the system.