| By modifying Palmer drought severity index based on meteorological data of 515 stations from 1957 to 2000 over China, characteristics of regional drought evolution were analyzed in spring.The results show that the summer drought index takes on descendant trend in the Inner Mongolian plateau area, the north part of North China and Changbaishan Mountain area, the Loess Plateau area, the Yunnan-Guizhou Plateau area and the plain of Northeast China, but it takes on ascendant trend in the Nanling Mountain areas, the Yangtze River area, the Yellow River and Huaihe River area, the Hexi Corridor area, the north of Tianshan Mountain area, the Talimu Basin area and the Qinghai-Tibet Plateau area.It is proved that the drought index exists 5～8 a period in the most areas, it exists 12～13 a and 15～16 a period in some areas, it also exists 20～25 a period in specific area.The east Asia summer monsoon is contrary bound up with the summer drought severity index of Northwest China and Qinghai-Tibet Plateau, but it is identical bound up with with the summer drought severity index of the Middle and East China. |