Abstract: Abstract: Background Drought, ranking among the most catastrophically destructive natural phenomena worldwide, manifests as a compounding environmental crisis through its escalating recurrence patterns and temporal endurance, thereby destabilizing critical ecological service mechanisms while simultaneously jeopardizing the sustainability of agroecosystem operations. Situated at the critical juncture of the southwest monsoon and plateau climate systems - a region characterized by intricate topographical variations and pronounced spatiotemporal precipitation heterogeneity - Yunnan Province has emerged as a focal point for ecological fragility research, where the synergistic interplay between complex orographic features and atmospheric circulation patterns creates a dynamic yet vulnerable environmental matrix. This transitional ecotone, further compounded by escalating climate change-driven meteorological extremes, manifests as a dual-status entity in China's environmental landscape: an ecologically sensitive zone exhibiting heightened susceptibility to systemic perturbations and a drought-prone hotspot where hydroclimatic anomalies demonstrate increasing frequency-intensity coupling. The province's unique geoclimatic configuration, marked by altitudinal gradient-driven microclimate diversification and monsoon-front modulated rainfall disparities, has been progressively destabilized through positive feedback loops between anthropogenic climate forcing and natural system responses, ultimately rendering it both a bellwether for regional climate change impacts and a paradigmatic case study in coupled human-environment system vulnerability. MethodThe water use efficiency of vegetation in Yunnan Province was calculated based on the total primary productivity (GPP) and land evapotranspiration (ET) data of medium resolution imaging spectrometer (MODIS) from 2001 to 2020. Combined with the standardized precipitation evapotranspiration index (SPEI), Theil-Sen trend analysis and Mann-Kendall significance test were used to evaluate the spatial and temporal variation trend of vegetation water use efficiency (WUE). Pearson correlation analysis was used to reveal the coupling mechanism between WUE and climate drought. Results:(1) The average annual ET and GPP in Yunnan Province were 530.88 mm and 611.08 g 大写 C 除 m 平方, respectively, which decreased with the increase of altitude, with significant vertical zonality, showing a distribution pattern of high in the south and low in the north. (2) WUE had a slight downward trend from 2001 to 2020, and extreme drought years had a significant impact on WUE. The annual average WUE of Yunnan Province was 1.51 g 大写 C 除 左圆括号 m m 点号运算符 m 平方 右圆括号 , which had obvious spatial differentiation characteristics. The WUE was the highest in summer and the lowest in winter. (3) Among the different vegetation types, the WUE of forest was the highest, and the WUE of grassland was the lowest. The average WUE of the four vegetation types was: forest > shrub > agricultural vegetation > grassland. The WUE of the four vegetation types showed a downward trend, and the forest decreased the most. (4) The positive correlation between WUE and SPEI in Yunnan Province increased with the increase of monthly time scale, and the long-time scale dominated the positive correlation. Conclusion The spatiotemporal heterogeneity of water use efficiency (WUE), shaped by drought stress, encapsulates vegetation's adaptive strategies to water deficits through coordinated physiological and biophysical regulation. These findings establish a scientific framework for optimizing water resource allocation and targeted ecological conservation in Yunnan Province, while offering critical insights into climate resilience planning and ecological security maintenance amidst increasing climatic variability.