Abstract:By using the rainfall data from NMC, the reanalysis data from NCEP/NC AR and OLR data from NOAA, the features of Asian summer monsoon, the western Nor th Pacific subtropical anticyclone (WPSA), ITCZ, Somalia Surges, Indian monsoo n and the heat sources in Asia Pacific area around the period of Jianghuai Valle y rainfall in 2008 are analyzed here to reveal the reasons for the anomalous features of Asian summer monsoon an d their influence on the beginning and ending of the rainfall and rainfall stren gth. The results show that forces of the monsoon members are complexly variable, decreasing or increasing by interacting with each other, so that no single memb er can play a predominant role, which is an important reason for the variable an d weaker rain belt of Jianghuai Valley. The movement of ITCZ is an important fac tor for the rainfall forecasting, it affects and precedes the WPSA by thermal an d dynamical mechanisms. Its abrupt strengthening at beginning of June is crucia l to bursting out of Jianghuai Valley rainy season and its strengthening and sur ging northwards with a typhoon landing at South China at the 5th pentad in the s ame month leads to the ending of Jianghuai Valley rainy season. So it is a criti cal forecasting index. Somali surges’ bursting out abruptly earlier than usual is also beneficial to the earlier onset of Indian monsoon and the beginning of J ianghuai Valley rainy season, and their persistence and recession have some infl uence on the position and intensity of rain belt. The onset of Indian monsoo n and the changing characteristics afterwards affect the position of India Burm a monsoon trough, which affect Jianghuai Valley rain belt by changing the st rength and distribution of heat sources over southern Qinghai Xizang Plateau an d Bay of Bengal.