Abstract: The characteristics of water vapor transfer over the East Asia summer monsoon region are studied by using NCEP/NCAR reanalysis data from 1958 to 1998. The results show that in summer there are four vapor inflow corridors to China: southwest corridor, South China Sea corridor, southeast corridor and northwest corridor. This shows that the impact of South Asia monsoon, South China Sea monsoon, subtropical monsoon and middle latitude westerly on summer rainfall anomaly over China, respectively. The four intensity indexes of water vapor transfer are defined and calculated, and their interannual variations are studied. Influencing areas of the four vapor inflow corridors to China are located by correlation analysis. Finally, the relationship between water vapor transfer anomaly and physical factors is discussed. The results show that the intensity of vapor inflow corridors is associated directly with atmosphere circulation anomalies, not with the same term SST.