Evapotranspiration (ET) in dryland ecosystems plays a crucial role in regulating regional water and energy balances as well as the carbon cycle against global warming and ongoing expansion of drylands. However, the current lack of systematic assessments regarding ecosystem responses to coupled meteorological and vegetation changes hinders a comprehensive understanding of ET regulation processes. This study quantified ET response thresholds and identified regulatory pathways within the meteorological-vegetation framework by analyzing 30 site-years of eddy covariance data collected from forest, grassland, wetland, and desert ecosystems in the dry-lands of China (2020-2022). The results showed that annual mean ET ranged from 147 mm in deserts to 541 mm in forests, following the order of forest > grassland > wetland > desert, while displaying distinct nonlinear responses to environmental factors. Air temperature (TA) and precipitation (P) were key drivers of ET across dryland ecosystems. ET in forests and grasslands was activated under moderate thermal conditions, whereas wetlands and deserts required higher heat accumulation. Although P thresholds occupied similar relative positions, deserts responded to moderate-to-small pulses while grasslands depended on larger event accumulation. Structural equation modeling and variance partitioning analysis further revealed that vegetation sensitivity to meteorological forcing decreased from forests and wetlands to grasslands and deserts. Consistent with this gradient, distinct regulatory pathways emerged: forests followed a meteorological-induction-vegetation-amplification pathway, wetlands exhibited a physiology-dominated pattern, grasslands followed a P-driven pathway, and deserts were governed by a meteorology-dominated pathway. These results suggest that differences in vegetation sensitivity help explain the shift in ET control from vegetation-mediated regulation to more direct meteorological forcing across dryland ecosystems. This study not only improves the understanding of ET regulation across contrasting dryland ecosystems but also provides critical threshold parameters and mechanistic insights for eco-hydrological modeling and the development of adaptive water resource management strategies.