Abstract: The Qinghai-Tibet Plateau is one of the most sensitive regions responding to the global climate change. Water environment has changed due to global warming in this area in the last few decades. The changed water environment has a great influence on the local hydrological dynamic processes and the terrestrial ecosystem. In this paper，monthly air temperature and precipitation data derived from 65 meteorological stations，and potential evapotranspiration （ET₀） and annual aridity index （AI） calculated using Penman-Monteith and arid index equation were employed to understand the water environment change in the Qinghai-Tibet Plateau. The changing trends of observed climatic factors （T and P） and calculated factors （ET₀ and AI） were analyzed using linear regression method，which were tested through Mann-Kendall test. Then，the relationship between climate change and water environment change was reanalyzed using Pearson Correlation analysis. Annual mean air temperature and annual precipitation showed the increasing trend with the rates of 0.038 ℃/a and 0.809 mm/a，respectively in the last four decades；ET₀ demonstrated a decreasing trend with a decaying rate of 1.215 mm/a；[AI] decreased and the climate is developing toward more humid status in most part of the area. The above mentioned pattern of the factors varied spatially. In the northern and western parts of the Qinghai-Tibet Plateau，T and P significantly increased，and ET₀ and AI significantly decreased. In the eastern and southern parts，T significantly increased，ET₀ and AI significantly decreased. The climate changing trend suggested a warmer and wetter tendency in northern part of the Qinghai-Tibet Plateau. It has been speculated that the significant decrease of ET₀ was probably the result of the lowering wind speed，although air temperature was increasing significantly. Meanwhile，the water environment in the Qinghai-Tibet Plateau also changed in the last few decades. Glaciers melted and shrunk significantly，especially in the eastern part of the Qinghai-Tibet Plateau. Lake areas changed differently because of different recharge conditions. In general，lakes expanded in the western part and kept stable in the eastern part of the Plateau，shrunk lakes distributed dispersedly. Hydrological data such as groundwater level，river runoff and soil moisture are very important for quantitative indicators of water environment change，in the term of water balance. Pearson Correlation analysis between the Qinghai Lake area and climatic factors recorded and computed from nearly four weather stations showed that，the Qinghai Lake area has a significant positive correlation with T，ET₀ and [AI] of Xining Station; has a significant negative correlation with T recorded in Gangcha Station，Qiabuqia Station and Guizhou Station，and ET₀ in Qiabuqia Station. It is obvious that the changed water environment has a close relation with the changed climatic factors such as T，P，ET₀ and AI，but the relationship between them is complicated，which requires more researches. At present，meteorological data and water environment data derived from weather stations and records are not precise enough to quantitatively draw a conclusion on the relationship between climate change and water environment change due to complicated topography，the quantity and distribution of weather stations and hydrologic stations. RS and GIS techniques and reanalysis data should be used in the future research.

Key words: the Qinghai-Tibet Plateau, climate change, potential evapotranspiration, aridity index, water environment