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Study region: Qinghai Lake Basin (QLB), the largest saline lake in China and its collecting basin Study focus: Climate change has caused clear shrinkage or dramatic water level fluctuation of lakes in arid and semi-arid regions, while the underlain mechanisms remain unclear. The joint lake-basin investigations (spatial) and long-term studies (temporal) are urgently needed. This study developed SWAT+ to jointly simulate the water cycle of QLB and investigated how the hydrological regime of QLB changed at the hundred-year scale. New hydrological insights for the region: The modeling framework consisted of the revised SWAT+ , reanalysis data, and reconstructed water level based on lake gravity core performed quite well (NSE > 0.9 for lake water level) in simulating the hydrological processes of QLB at the hundred-year scale (1910 – 2018). Temporally, decadal variations of hydrological components in QLB decreased in sequence of precipitation (46.33 mm), lateral flow (26.85 mm), evapotranspiration (16.03 mm), snowmelt (10.44 mm), groundwater flow (5.66 mm), and overland flow (1.18 mm). Spatially, precipitation, water yield, lateral flow, and groundwater flow in upstream regions of QLB, where the precipitation amount was small, were most sensitive to climate change. The long-term water level decrease of Qinghai Lake during 1928 – 2003 was mainly driven by variations of river runoff and lake surface evaporation; the clear water level increase since 2004 was dominated by river runoff changes.