Abstract: The onset process of Asia summer monsoon during 1983 is analysed and the independence and the relation between India monsoon and South-China sea monsoon are studied by using ECMRWF data. The results show that there are independent centers of seasonal variation in India monsoon region and、 in Sonth-China sea monsoon region respectively; the beginning dates, the physical mechanisms of monsoon onset and the relation between wind and temperature or humidity during the onset process in India monsoon region are different from those in South-China sea monsoon region; after the onset, the variations of the monsoon circulations and the physical processes which maintain monsoon and its temperature and humidity fields in the tow sub-monsoon reginos tend to consist with each other; vertical movement plays an important role in the relation between the two sub-monsoons.