Abstract: Based on the thermodynamic charactristics of the summer monsoon and the change of the lower layer wind fields, the relation between the early summer flood periods of southern China,including the first flood period of South China and the plum rains period of the middle-lower reaches of Yantze River and the activities of the summer inonsoon is analysed. The establishment processes of the summer monsoon circulation of East Asia are investigated. It is shown that the beginning and ending of the flood periods are exactly in accordance with the arrival and leave of the fore boundary of the summer monsoon. The establishment processes of the monsoon circulation from the very beginning of the arrival of the monsoon to the period of great prosperity of development are not the same for each year. They can be classfied into four categories. Each category may have four or three stages. And then the structure of the summer monsoon regime of East Asia is not unitary. There exist four types of structure model of the monsoon regime of East Asia.