The interannual and intermonthly variation of the water vapor and its mean transfer in the atmosphere over Northwest China are calculated and analyzed by using the NCEP/NCAR global reanalysis grid data(2.5°×2.5°Lat/Lon) for 43 years (1958-2000). The results show that: (1) The climatic averaged water vapor in whole air column over Northwest China is concentrated in the east and west areas, respectively, with the maximum in summer and the minimum in winter. In the east areas water vapor is most abundant an...