Alpine grasslands (AG) exhibit significantly higher Humidity Index (HI) than temperate grasslands (TG), leading to a marked moisture gradient variation along the Chinese Grassland Transect (CGT). Over the past few decades, numerous eddy covariance sites have provided valuable insights into evapotranspiration (ET) dynamics at the site scale. However, the spatial patterns of ET and it dominate factors along the moisture gradient across the CGT remain poorly understood. This study integrates observational data from 48 eddy covariance sites (2003---2020) and remote sensing products to analyze the spatial distribution of ET and its driving mechanisms along the CGT. The observational results showed that the mean annual ET in AG (454 f 119 mm) was significantly higher than that in TG (320 f 115 mm), which was consistent with their respective HI. The decoupling coefficient (Omega) increased with ecosystem wetness, being significantly higher in AG (0.41 f 0.11) than in TG (0.23 f 0.10). This suggests that in arid regions, the vapor pressure deficit (VPD) may have a stronger influence on ET than net radiation. As ecosystem moisture gradient change, grasslands have evolved different adaptation mechanisms. Compared to TG, AG exhibited higher canopy conductance and greater sensitivity to changes in VPD. However, the sensitivity of the ratio of transpiration to ET to canopy conductance was lower in AG than in TG. This may reflect a more sensitive water conserving response in TG, where stomatal closure leads to a stronger reduction in transpiration, thus minimizing water loss under arid conditions. This study investigates the spatial variability of ET across the CGT and its environmental controls, providing insights into grassland ecosystem responses to future climate change.