Abstract: The thesis, having analysed the variations in atmospheric energy over a domain bounded by 95°and 120°E, and 0°and 25°N during the periods of April to June of both 1980 and 1981, reveals the fact that the horizontal energy divergences and the horizontal energy distributions over that domain changed notably during the onset processes of the summer monsoon over East Asia, and reflected relatively the early and late beginnings of the onset and the differences of strength. The calculations show that latent energy is a significant factor of the onset processes of the summer monsoon over East Asia.The thesis also makes a preliminary study on the dynamic expressions of the interaction between the middle and lower latitude circulations before the onset, and points out that the southward transportation of eddy momentum across 35°N triggers the onset of the summer monsoon over East Asia.