Abstract: Based on the ECMWF and NCEP/NCAR re-analysis of the climate data during the 38 years(from 1979 to 2016),the spatial and temporal distribution and the transportation of the water vapor in the northwestern China were analyzed.The results show as follows:(1) The water vapor content in northwestern China was increased from the middle 1980s to the late 1990s,but it was decreased after that.In terms of seasonal disparity,the water vapor content reached its maximum value in summer,accounting for 46.6% of the annual average water vapor content. (2) The spatial distribution of the water vapor in the northwestern China is in accordance with that of the precipitation in the form of "lower value in the middle and high values on both east side and west side" which meant that the water vapor was accumulated mainly in the east part of the region and in the Tianshan Mountains and east Tarim Basin in the west part of the region with its content being 12-30 mm,and there was less water vapor in the middle of the region with the content less than 10 mm. (3) The west wind and monsoon were the main carriers for the water vapor circulation in the northwestern China.The zonal westerly wind transferred the water vapor at 100-500 kg·m^-1·s^-1 which dominated the transportation of water vapor in a year.The southwest monsoon from the Indian Ocean in summer had a great effect on the water vapor transportation in the east of the region with a transport intensity being 100-500 kg·m^-1·s^-1. (4) The water vapor sources were primarily distributed in the Tianshan Mountains,the middle and east part of Qinghai Province,the middle and west part of Hexi Corridor,Ningxia Province and the north part of Shaanxi Province while the water vapor sinks were located in the south part of Gansu Province and the south part of Shaanxi.

Key words: water vapor content, spatial and temporal distribution water, vapor transportation, northwestern China