###### Abstract  
Water-use efficiency (WUE) is an important indicator for understanding the coupling of carbon and water cycles in terrestrial ecosystems. It provides a comprehensive reflection of ecosystems' responses to various environmental factors, making it essential for understanding how ecosystems adapt to complex environmental changes. Using satellite-based estimates of gross primary productivity (GPP) and evapotranspiration (ET), our study investigated the spatiotemporal variations in WUE across China's terrestrial ecosystems from 2001 to 2020. We employed the geographic detector method, partial correlation analysis, and ridge regression to assess the contributions of different factors (temperature, precipitation, solar radiation, vapor pressure deficit, leaf area index, and soil moisture) to GPP, ET, and WUE. The results show significant increases in GPP, ET, and WUE during the study period, with increase rates of 6.70 g C m\({}^{-2}\) yr\({}^{-1}\), 2.68 kg H\({}_{2}\)O m\({}^{-2}\) yr\({}^{-1}\), and 0.007 g C H\({}_{2}\)O m\({}^{-2}\) yr\({}^{-1}\), respectively. More than three-quarters of the regions with significant trends in WUE (\(p<0.05\)) displayed notable increases in WUE (\(p<0.05\)). Among all driving factors, leaf area index (LAI) made the largest contribution to WUE, particularly in warm temperate semi-humid regions. Precipitation and solar radiation were the primary climatic influences in arid regions of northern China and humid regions of southwestern China, respectively. water-use efficiency; gross primary productivity; evapotranspiration; climate change; China 2020 IEEE/RSJ International Conference on, 2020, Vol., 2020, Vol. In recent years, remote sensing has become essential for estimating and studying WUE, offering large-scale, high-resolution data with temporal and spatial depth [12]. The Moderate Resolution Imaging Spectroradiometer (MODIS), providing long-term continuous GPP and ET data products, is particularly valuable for analyzing WUE's spatial and temporal dynamics and its relationships with various driving factors. Recent studies have revealed significant seasonal and interannual WUE variations, crucial for understanding ecosystem responses to environmental changes [13; 14; 15; 16]. WUE is controlled by vegetation characteristics including stomatal conductance and intercellular CO\({}_{2}\) concentration, as well as community structure [17; 18; 19; 20], which are also influenced by various environmental factors. Climatic factors--temperature (TEM), precipitation (PRE), solar radiation (RAD), and vapor pressure deficit (VPD)--are primary factors impacting WUE in vegetated ecosystems. Both TEM and RAD have critical thresholds, below which WUE increases with either factor, but decreases once these thresholds are exceeded. Notably, the critical values vary across ecosystems due to differing environmental impacts [21; 22]. Moderate increases in precipitation generally enhance WUE, while excessive precipitation can suppress it [23]. The influence of meteorological variables also varies with regions; for instance, WUE increases with RAD at higher latitudes [24]. The relationships between PRE and WUE exhibit distinct characteristics across different temperature zones [25; 26]. Specifically, strong interrelationships between PRE and WUE exist in regions with sufficient heat, while temperature dominates WUE north of 50\({}^{\circ}\)N latitude [27]. The increase in global temperature correlates with an increase in VPD, triggering shifts in enzymatic activity within plants, increase transpiration rates and decrease net photosynthesis rates. These alterations impact vegetation growth processes, culminating in a decline in WUE [28; 29]. With the intensification of global climate change, in-depth analysis of WUE and climate factors is essential to understanding ecosystem resilience and managing water resources effectively. China's rapid economic growth, coupled with global warming, has intensified the complex interactions between human activities and terrestrial ecosystems.