[Objective] The water use efficiency of typical woody plants at different slope positions in karst slope habitats were analyzed in order to provide guidance for formulating effective soil and water conservation and ecological restoration measures for karst slopes. [Methods] Using meteorological data， soil mass moisture content， and stable isotope （δ2H， δ 18O， δ13C） data， the water sources and water use efficiency of typical woody plants in three different slope plots in the karst trough valley of Mingyue Mountain， Chongqing were studied. [Results] ① Soil moisture content was higher during the rainy season than during the dry season. In terms of slope position， the average soil moisture content on the upper slope was lower than that on the middle slope， with a difference ranging from 5.07% to 28.41%， and approximately 16.36% to 30.49% lower than that on the lower slope. ② Water from the surface karst zone serves as a critical water source for woody plants at different slope locations. The utilization rates were 34.65%， 25.58% and 20.82% for the upper， middle and lower slopes respectively， during the rainy season， and increased to 54.44%， 53.60% and 43.47% respectively， during the dry season. During the rainy season， the utilization ratio of soil moisture by plants in the 20—40 cm soil layer on the middle and lower slopes was higher than that on the upper slopes. During the dry season， the proportion of soil moisture utilized by plants in the 20—40 cm soil layer on the lower slopes was higher than that on the upper slopes.③ The δ13C values and intrinsic water use efficiency （WUEi） of trees and shrubs were lower during the rainy season than during the dry season. Across different slope positions， the WUEi of trees was higher than that of shrubs， with the mean WUEi following the order： upper slope > middle slope > lower slope. [Conclusion] Owing to differences in slope position， the soil moisture content in the karst trough valley increases from the top to the bottom of the slope. When plants on slopes are exposed to water stress， they make greater use of the water in the surface karst zone and exhibit higher water use efficiency.