Water use efficiency (WUE) is an important index to deeply understand the ecosystem carbon and water cycle and their coupling relationship. However, as one of the important forest types in China, the research on the WUE spatio-temporal pattern and its driving mechanism of bamboo forest is insufficient. In this study, we obtained WUE in bamboo forest areas from MODIS net primary productivity (NPP) and evapotranspiration (ET) data, used the linear trend method to calculate the interannual rate of change of WUE to characterize the change trend, and applied the geographically weighted regression (GWR) model to analyze the relationship between WUE and 10 driving factors, including climate and topography, to explore the WUE driving mechanisms in bamboo forest areas in southern China in 2000-2019. The results showed that:(1) the multi-year mean value of WUE in the bamboo forest areas of southern China was 0.89 gC m^-2 mm^-1 from 2000 to 2019, showing a decreasing trend, with an average annual decrease of 0.0028 gC m^-2 mm^-1, because the rising rate of evapotrans piration was greater than that of net primary productivity; WUE showed a spatial distribution pattern of high in the south and low in the north, with 83.5% of the area showing a decreasing trend. (2) The analysis of WUE drivers based on the GWR model showed that the strongest drivers of WUE were CO₂ concentration and annual precipitation, while the topographic factors such as elevation and slope had a weaker driving effect, and human activities had a smaller positive driving effect on WUE in most areas. This study clarifies the response patterns of bamboo forests to climate and environmental changes in China, and provides a scientific basis for the development of adaptive management measures for bamboo forests, and for better utilization of bamboo forests in mitigating climate change.