Based on Jiangsu Taihu lake basin (1956-2012) rainfall, the paper analyzed the runoff and its time and space variation in Taihu lake basin and studied the runoff of the basin of inter-annual variations and the relationship between the two.The results showed that all of rainfall and runoff present growth trend. Every ten years the average rainfall increases 29mm, average runoff every ten years increase 26mm; on seasonal distribution of rainfall during the year, summer and winter show a tendency of increase, spring and autumn a tendency of decrease; the increase of the unequal distribution of rainfall during the year result in more uneven distribution of runoff throughout the year. Runoff concentrated in the flood season and flood runoff amounts to about 84.8% of annual runoff, witch increase the flood and drought risk during a certain season.