Abstract: In order to well-understand dry and wet climatic conditions in the northwest part of Tibet, this study investigates the distribution and its variation tendency of climatic water budget in above region based on the meteorological observation in the past 30 years along with Penman-Monteith equation. Results show that the variation of water budget in the study region generally exhibits deficit tendency in its spatial distribution. Whatever the annual or the seasonal water deficit, all of them gradually decrease from the west to the east part. The annual and seasonal water deficit expresses decreasing tendency in the north part of Tibet which shows that water deficit has assuasive trend during 1980-2009. The most noticeably water deficit decrease appears in summer, then followed by that in spring and the amplitude reduction of water deficit in autumn is the smallest. The annual water budget and that in summer and winter persists significant sudden change. The water budget is negatively related to the air temperature, wind speed and sunshine duration while positively related to the relative humidity and precipitation. As a whole, increasing precipitation, decreasing sunshine duration and wind speed might be the major meteorological reasons to the decrease of water budget.