Abstract: In this paper, the change of surface water vapor was analyzed using the linear trend estimation, anomaly analysis, Mann-Kendall sharp change test and power spectrum analysis based on the data of water vapor pressure at 44 meteorological stations in the Tianshan Mountains during the period from 1961 to 2009. The results show that the change trend of surface water vapor in the Tianshan Mountains was significant, and the average change trend was 0.015. There were the obvious inter-annual and inter-decadal differences in variation and change trend of annual and seasonal surface water vapor, the highest increase occurred in the late-1990s, the minimum in the late-1970s and mid-1980s, and the maximum in the early 21st century. The increase trend of surface water vapor was the most significant in summer, then in autumn and winter, and the minimum increase occurred in spring. Sharp changes of the annual and seasonal surface water vapor occurred in 1986 (especially in summer and autumn), 1980 (winter) and 1996 (spring). The test shows that all the sharp changes were significant( r=0.05).The power spectrum analysis shows that there were the obvious periodicities in annual and seasonal surface water vapor change. The obvious annual periodicities of surface water vapor change were for 3.2 years and 2.9 years; the summer ones for 2.9 years and 2.3 years, and autumn ones for 3.6 years and 3.2 years. The change trend and sharp change of surface water vapor in the Tianshan Mountains were similar to the change trends of mean annual temperature and precipitation, westerly circulation, Qinghai-Tibetan Plateau circulation NAO and the time of their sharp changes. The correlation between annual precipitation and water vapor was the closest, and followed by temperature and other factors. 

Key words: global warming, surface water vapor, climate change, precipitation, water circle, Tianshan Mountains, Xinjiang