Jiangsu summer representative drought or flood year is classified by s tudying evolvement character of Jiangsu summer precipitation space-time distribu tion with EOF. The result indicates during recent twenty years, the drought or f lood ye ars of entirely province relatively decrease, and that the regional drought or f lood years increase. Moreover, by studying prophase variety character of the Northwest Pacific subtropical high pressure its effect on the change of distribu tion of summer drought and flood in Jiangsu is analyzed.