Abstract:Based on the summer daily observations from 67 stations in Jiangsu during 1961-2011, using the daily rainfall amount at different levels, the summer rain days of Jiangsu for nearly 51 years were analyzed with trend analysis, mutation analysis and wavelet analysis. The study found that all of rain days at different grades present obvious character of distribution in northwest-southeast direction, and Huaihe river is an important dividing line of the spatial and temporal distribution at different grades of rain days in Jiangsu in summer; along with obvious interannual and decadal changes, rain days at all levels have mutation characteristic as well as the interannual oscillation cycle of quasi-6-year and decadal oscillation cycle of quasi-12-year with different major periods of presence; the days with trace amount of rain are decreasing while rain days at other levels are increasing. The trend contribution of rain days at various levels to effective rain days is analyzed: the downward trend of effective rain days in north Jiangsu mainly results from decreasing of heavy and torrential rain days, while the upward one in central and south Jiangsu is attributed to the increasing of light, heavy and torrential rain days.