<p>Water use efficiency (WUE), as an indicator for plants to regulate water physiological processes through photosynthesis, is a key link between carbon and water cycling in ecosystems, reflecting the rapid adaptation strategies of vegetation ecosystems to site environment and resource changes. In this study, satellite data and ground-based observation data from 2001 to 2020 were developed to simulate and estimate the spatial distribution characteristics of WUE in different functional zones and analyze the time lag and cumulative effects of climate on vegetation. The results show that: (1) From 2001 to 2022, the multi-year average WUE in the Shiyang River Basin (SRB) was 0.99 gC·kg^-1 H₂O, exhibiting a spatial pattern of high values in the middle reaches and low values in the upper and lower reaches, with the highest value in Area II (1.23 gC·kg^-1 H₂O) and the lowest in Area IV (0.80 gC·kg^-1 H₂O). On a monthly scale, WUE showed an increasing trend in February and from November to December, and a decreasing trend in the remaining months. (2) Annually, WUE was significantly negatively correlated with air temperature and precipitation. However, the monthly responses varied significantly: WUE was positively correlated with air temperature from September to March and negatively correlated from April to August; WUE was negatively correlated with precipitation in all months, with the strongest negative correlation in June. Zone III was sensitive to air temperature, while Zone II responded more significantly to precipitation. (3) WUE responded to temperature changes with an immediate response (91.59% of the regions with a lag of 0 months), whereas it relied on a 3-month cumulative effect for precipitation (TLA0-3). The southwestern part of Region I exhibited a different lagged and cumulative response to climatic factors compared to other regions due to the cold and desert environments.</p>