Abstract: Based on T_BB data from Meteorological Institute Research of Japan,a study is carried out of the features of seasonal transition of Asian-Australian monsoons and Asian summer monsoon establishment,indicaaing that the transition begins as early as April,followed by abrupt changes in May-June; the Asian summer monsoon sitUation is fully established in June. The winter convective center in Sumatra moved steadily northwestward across the "iand btidge"of the maritime continent and the Indo-China Peninsula as time goes from winter to summer,thus giving rise to the change in large scale circulations that is responsible for the summer monsoon establishment over SE Asia and India; the South China Sea to the western Pacific summer monsoon onset hats a close relation to the active convection in the Indo-China Peninsula and the steady eastward retreat of the subtropical high-valued T_BB band,corresponding to the western pacific subtropocal high.