Abstract: The factor analysis and the orthogonal rotation method under varimax criterion are used to calculate and identify out four high loading regions of precipitation and their factor score coefficients in the flood season (May-Sep.) over middle and lower reaches of the Yangtze river. Their spatial and temporal variations are characterized by the natural synoptic scale precipitations over the reaches. The Eastem Pacific Equatorial SST, the mean SST's for other sea regions and the ENSO events are all associated to a certain with the regional precipitation anomaly in the flood season. The results obtained may be used as reference factors for short-range prediction of flood season's precipitation.