Abstract: Based on the experiences of the European International Radar Network and the British NIMROD system and according to actual condition in China, a large area rainfall observation in real-time automatic system (called LARORAS) has been developed by using digitized radar network in middle reaches of Yangtze River and GMS satellite as the main technical methods and incorporating numerical wind field prediction, in which the processing technique in real time for quantitatively measuring and estimating large area rainfall accumulation over the Yangtze River valley has been successfully developed, its products have great values for preventing flood and construction of large reservoir engineering.