Based on NCEP reanalysis data, the characteristics of the moisture transfer over the Jianghuai Valley during the summer of 2003 are studied. The results show that the exceptional precipitation of the Jianghuai Valley in the summer of 2003 is related to the exceptionally intense moisture transfer in the southern area of China. And the Bay of Bangle and the South China Sea are two main moisture sources for the sustained heavy rain over the Jianghuai Valley. The calculation result of the heavy rain event shows that the budget of the moisture over the Jianghuai Valley and the attribution of two main moisture sources varied at different layers. At the layer of 1000—850hPa, which is the main moisture convergent layer during the heavy rain event, the South China Sea is the most important moisture source.