Study region: China's arid and semi-arid regions Study Focus: Global vegetation greening has increased evapotranspiration and enhanced transpiration' role in the land-atmosphere water cycle. Yet in arid regions, how greening affects this cycle remains unclear under coupled soil moisture (SM) and vapor pressure deficit (VPD). To address this, we used the transpiration-to-evapotranspiration ratio (T:ET) to represent transpiration's contribution and quantified its sensitivity to vegetation change as mu =TrendT:ET developed a classification framework combining SM and VPD trends with baseline temperature to assess T:ET sensitivity to greening across hydroclimatic conditions. New Hydrological Insights for the Region: We observed a widespread decline in T:ET sensitivity to LAI change across China's arid grasslands, with the sensitivity dropping from 30 to near 0 % m2m-2 in High-Ta zones and from 20 to near 0 %m2m-2 in Low-Ta zones. In SM up arrow VPD) regions, LAI exceeded the boundary damping thresholds (1.189 m2m-2 in High-Ta, 1.024 m2 m-2 in Low-Ta), indicating reduced sensitivity was mainly due to this effect. In SM up arrow VPD up arrow regions, LAI remained below thresholds (1.054 m2 m-2 in High-Ta, 1.628 m2 m-2 in Low-Ta), so the decline was primarily driven by increased VPD. Higher VPD enhanced transpiration in Low-Ta zones with lowbaseline-VPD but suppressed it in High-Ta zones with high-baseline-VPD. These results highlighted vegetation's critical role in regulating the land-atmosphere water cycle in temperature arid grasslands and underscored atmospheric aridity's pronounced influence in sparsely vegetated areas.