Areal Precipitation is an important parameter in Hydrometeorology. The e stimatio n and prediction of areal precipitation are directly concerned with the accuracy of flood forecast and the decision making for flood dispatching. Owing to the c omplexity of spatial pattern of rainfall, how to accurately estimate areal preci pitation still remains a scientific problem. Traditionally spatial analysis tech niques are applied to regular precipitation data to estimate the areal precipita tion. With the development of nonregular observational technologies, areal pre c ipitation estimation based on data assimilation of radar and satellite data comb ined with automatic raingauge data has been the trend of areal precipitation est imation technology, while integrated management of data analysis and display bui lt on GIS has been the mainstream of the operational system of area rainfall est imation. Through the comparison between hydrologic simulation and observation, t he estimated areal precipitation can be indirectly validated.