Abstract: Climatological characteristics of moisture transport over the Yangtze River basin during summer monsoon are investigated based on NCEP/NCAR reanalysis data for the period of 1973—1998. The differences between drought and flood years, and especially some features of moisture transport over the Yangtze River basin in the course of flood in 1998 are examined. The results show that the characteristics of horizontal moisture transport over the Yangtze River are different from month to month. Moisture transport from the Bay of Bengal and South China is main sources of the Yangtze River basin precipitation. Droughts or floods over the Yangtze River are closely related with the onset time of summer monsoon over the South China Sea. Yangtze River basin floods chiefly resulted from the long-term maintenance of moisture transport from the South China Sea and the Bay of Bengal to the Yangtze River basin in 1998.