As an important part of land water resource, lake is an important indicator of local climate and global environment change. The increase of lake area and change in the lake's water level directly reflect the process of water balance change in its basin,which is sensitive to regional and global climate change. Qinghai Lake is the largest saline lake in China,with 3 190 m asl in the arid-semiarid area of the Qinghai-Tibet Plateau. The lake has experienced decline in water level and lake area over the past 50 years,but it has rebounded over the latest 10 years. This study investigated lake hydrology,climate change and hydrothermal and vegetation growth conditions in the basin, focusing on the causes for water level variation. To reveal hydrology,meteorology and vegetation change, linear trend method was used to analyze long-term data in this study. The Pearson correlation coefficient method was used to calculate relationship between various factors and the lake water level to quantitatively evaluate the lake water level change effected by regional meteorological,hydrological,and vegetation factors. The results showed that the basin climate had a significant warming and wetting trend,and the total precipitation had a weak increase trend with a climatic tendency rate of 10. 8 mm·(10 a)~(- 1) . The annual evapotranspiration rate and annual actual evapotranspiration fluctuated greatly in the basin. Average net primary productivity (NPP) of the basin was 2. 86 t DM· hm ~(- 2)·a ~(- 1), showing a significant increase trend (P < 0. 01) . The water level was dropped during the period from 1961 to 2003,and was significantly increased from 2004 to 2015 with an increasing rate of 14. 4 m·(10 a)~(- 1) (P < 0. 01) . The trend of warming and wetting of the climate was intensified and the runoff into the lake got increased, resulting in a significant rise in water level. The vegetation growth is improved and NPP is significantly increased. The amount of precipitation, the accumulated temperature (above 0 degree Celsius) ,annual air temperature, runoff, NPP and evaporation in the year before had even bigger impact on the lake's water level in current year. The increase of the NDVI and NPP reflected the improvement of the vegetation growth in the basin which in return enhanced the capability of the basin in the conservation of water and soil, indirectly impacting the lake's water level. The precipitation, the accumulated temperature (above 0 degree Celsius) ,air temperature, runoff and NPP had a positive feedback effect on the lake's water level,while evaporation has a negative feedback effect on the lake's water level. The annual precipitation and runoff were the most direct factors of the water level changes.