There existed the characteristics of short period and less rainfall during the Meiyu in 2005,which made the main rainband occur in the Jiangnan area and South China.The relationship between the 100hPa circulation and Meiyu is analyzed based on the NCEP /NCAR reanalysis datasets in 2005.The results show that the center of 100hPa South Asia high stayed over the south of the Qinghai Tibetan Plateau in June,the ridge position at 120°E was located in 21—26°N,it is obvious that the ridge position is southerly in June.The center of South Asia high moved northward in July.During June to July,the ridge position of the 100hPa South Asia high at 120°E is northerly by five latitude degrees or so more than that of the northwest Pacific subtropic high.Both east ridge position of the 100hPa South Asia high and the ridge of the 500hPa subtropic high move northward and southward synchronously,while the north of east ridge position of 100hPa South Asia high corresponds the place where the heavy rain occurs.