Abstract: Based on the sounding data from 14 sounding stations over the Qinghai-Tibet Plateau during the period of 1979-2008 and the NCEP/NCAR reanalysis data in recent 30 years, the spatiotemporal distribution of water vapor content over the plateau in summer and the factors affecting abnormal water vapor content were analyzed using the means of linear trend method, Mann-Kendall test and composite analysis. The results show that water vapor content over the plateau in summer was decreased with the increase of altitude, namely water vapor content was high over the southeastern and northeastern parts of the plateau but low over the northwest part; On the whole, water vapor content over the plateau in summer was in an increase trend in recent 30 years, especially over the arid western region. The characteristics of the years with high (or low) water vapor content over the plateau in summer were as follows: （1） Water vapor flux was converged (or diverged) in the years with high (or low) water vapor content; （2） The potential height of water vapor content over the low-level plateau was in a negative (or positive) anomaly in the years with high (or low) water vapor content; （3） Surface temperature was higher (or lower) in the years with high (or low) water vapor content.

Key words: water vapor content, spatiotemporal variation, atmospheric circulation, surface temperature, Qinghai-Tibet Plateau