Abstract: The diagnoses and analyses of Asia summer monsoon in 2001 are made by means of Black-body temperature (T_BB) from Japanese GMS. It is concluded that there are three summer monsoon onsets over the Indochina Peninsula and the South China Sea, and the intensities are stronger than those in the same period of history. The results reveal the characteristics of monsoon onsets and lulls in the three monsoon regions (India-Bengal Bay, Indochina Peninsula, and South China Sea). Analysis is also made on the influence of monsoon on the three heavy rains (from the beginning of June to the middle June, the end of June to the beginning of July, and the end of August respectively) in the South China and the middle and lower reaches of the Changjiang River. The result shows: it is the essential condition of large-area and long-time heavy rainfall over the Southeast China that the monsoon onsets combine with the cool air from the North. According some important clues are provided to make forecast of heavy rainfall in the region.