Abstract: Using the enhanced vegetation index (I_EV) and land surface temperature (T_LS) dataset derived from the TERRA/MODIS (Moderate Resolution Imaging Spectroradiometer) synthetic products MOD13 A2 (16-day composite,in DOY (Day of Year) 161-240 between 2001 and 2010,and DOY 145-288 in 2009) and MOD11 A2 (8-day composite,the same items of products with MOD13 A2),the T_LS-I_EV two-dimensional characteristic space can be constructed.The I_TVD (temperature-vegetation drought index) is then extracted to indicate the top-soil moisture of northern Tibet.The intra-annual and inter-annual variations of soil moisture on the northern Tibetan Plateau are respectively analyzed for the 2009 growing season and the summer seasons (2001-2010).The results show that the intra-annual variation of T_LS-I_EV slope and the slopes of dry-edge and wet-edge will be smaller with the increase of vegetation cover,which indicates the buffering effect of vegetation on in environmental temperature changes.The intra-annual variation of top-soil moisture on the northern Tibetan Plateau appears to be significant.The variation is mainly due to the seasonal changes in temperature,precipitation,vegetation cover and frosting and ice-out of frozen soil.The droughty tendency in study area is detected in the variation of soil moisture in the last decade.However,the tendency appears to be varying in different climatic zones of the study area.The mean summer temperatures at seven weather stations in northern Tibet reveal a significant upward trend.The observed precipitation in the eastern region of northern Tibet suggests a slight downward trend.The inter-annual variations of precipitation can be observed at other stations.Furthermore,the inter-annual variability of soil moisture is in agreement with that of mean summer temperatures.