Abstract: Using a global spectral model T42L11 the sensitivity experiments to a rainstorm process during period of June 26~July 1, 1991 are performed. The results show that if the vapour sources from Indian Ocean to the Bay of Bengal (to the west of 100°E) were strong cut down, East Asia monsoon circulation would be weakened, and Meiyu precipitation be reduced; on the contrary, when the moisture sources from West Pacific to the South China Sea (to the east of 100°E) were decreased, East Asia monsoon circulation would be strengthened, and the rainfall belt would move over to North China.