Abstract: Based on the radiosonde data observed two times a day for 125 stations in China,the total transport,eddy transport and divergence fields of water vapour are calculated and analyzed for the whole atmospheric layer over the Yangze River Valley during two typical wet/drough summers (1980/1985),when there were three currents that carried water vapour steadily from the southwest,northwest and southeast respectively,and then joined together over the Yangtze River Valley,high precipitation would appear near a convergence belt,yielding floods and water-loggings.On the other hand,during drought period,the three currents are weak and unstable,so that the condition of convergence belt formation cannot be met.Eddy transport also has similar feature.Water vapour transport due to a strong and stable current from the southwest,is a main source of precipitation.