Abstract: Based on observational station data in the Haihe River basin, NCEP/NCAR reanalysis data and JRA-25 data, the change of water vapor content, and water vapor budget and transport in summer over the Haihe River basin from 1951 to 2008 are studied. The results show that water vapor content over the Haihe River basin has obvious interdecadal variations, and is significantly correlated with precipitation. The zonal water vapor transfer to the Haihe River basin occurs mainly between 850 and 700 hPa, while the meridional water vapor transfer mainly happens below 850 hPa. The southerly strong moisture transfer belt below 850 hPa is the primary contributor of water vapor for the Haihe River basin, and also the major influential factor for precipitation in the basin. The influences of cyclonic pattern and south wind patterrn circulation upon the water vapor content are the most significant.