Global climate change is profoundly reshaping the hydrological cycles of ecosystems worldwide, heightening the need to understand how these systems respond to shifts in ecohydrological processes. A key indicator in this regard is the critical soil moisture threshold (Bcrit), which marks the transition from unstressed plant water use to moisture-limited conditions. This study provides a systematic analysis of the spatiotemporal patterns of Bcrit across diverse ecosystems in China from 1980 to 2020. Our findings reveal a general decline in Bcrit across most ecosystem types over this period. Notably, however, in northwest China and the Qinghai-Tibetan Plateau, Bcrit exhibited an increasing trend, contrasting with declines observed in other climate zones. At the land-use level, Bcrit decreased in most classifications, with the exception of Open Shrublands and Barren areas. The mechanistic analysis identified that vapor pressure deficit dominated the Bcrit variations in arid and semi-arid zones, while precipitation was the primary factor in more humid regions. In the Qinghai-Tibetan Plateau, solar radiation had a primary negative impact on Bcrit. In the subtropical or tropical humid south of China, the water deficit index was the main negative driver. A comparative analysis reveals a marked shift in the influences of key climatic drivers on the Bcritbetween the two periods (1980-2000 and 2001-2020). The positive effect of precipitation was enhanced, while the inhibitory effect of vapor pressure deficit was reduced. Concurrently, the sensitivity of Bcrit to both water deficit and actual evapotranspiration declined across most regions, suggesting a weakening influence of these factors. Moreover, the negative effect of maximum temperature intensified notably in northern and northwestern China, likely due to enhanced soil moisture depletion and increased atmospheric evaporative demand under warmer conditions. This study provided a theoretical framework for assessing ecosystem adaptability and informing water resource management.