Abstract: Based on data of July and August for years 1974-1977,the general circulation in the equatorial regions from south China Sea to the West Pacific is studied. It is found that, so far as the climatological average is concerned, the East African low-level jet can influence the south parts of India, Bay of Bengal, Indo-China, and South China Sea. In this regions, the interannual changes of monthly mean intensity of southwest monsoon are consistent with each other. There is a channel of cross-equatorial flow located at about 15°E near the east coast of New Guinea, while in the area of 110-140°E equator there is no strong and consistent southerly cross-equatorial flow. To the east of New Guinea, the air from Southern Hemisphere crosses the equator and turns to southwesterly flow blowing in the Nerthwestern Pacific. The topographical influence of the high mountains in New Guinea is the important cause of the excistence of this cross-equatorial flow. Tt is found that the southwest monsoon in the southern parts of Indo-China and South China Sea mainly comes from southern India and Bay of Bengal, it does not directly comes from the Southern Hemisphere.But the southwest monsoon in tropical Nerthwestern Pacific comes directly from Southern Hemisphere. The intensity of the southerly component of cross-equatorial flow near the east coast of New Guinea closely relates to the intensity of the southwest monsoon in the tropical Nerthwestern Pacific. Hence, the southwest monsoon to the south about 15°N from Southern Asia to Nerthwestern Pacific consists of two branches of air flow, one is the East African low-level jet, which flows from southern India to South China Sea, and the other comes from the Southern Hemisphere crossing equator near 150°E.