Abstract: A unique but very common habitat, rocky outcrop in Karst region of southwest China was selected for this study. Sap flow patterns of two typical tree species (Radermachera sinica and Triadica rotundifolia) were analyzed by using the method of Granier’s thermal dissipation probe (TDP). The results showed that sap flow density of both species exhibited clear response to the wet and dry seasons. However, the absence of sap flow only last about 1 month for R. sinica but 4 months for T. rotundifolia, despite the same functional type of these two species. T. rotundifolia consumed relatively higher annual total amount of water per unit area at breast height than R. sinica. Moreover, water that was consumed during the growing season (from April to September) accounted for 90% and 66% of the annual total amount for T. rotundifolia and R. sinica, respectively. Sap flow densities of the two species were very significantly positively correlated with photosynthetically active radiation, water vapor pressure deficit, and temperature, while had very significant negative correlation with air relative humidity. Sap flow densities and daily water consumptions of two tree species were not only lower than the tree species distributed in the same climatic non-karst zone of the study area, but also lower than the main tree species in karst area nearby, and even lower than the typical species in dry area with extremely low precipitation. The above results suggested that water consumption of the two tree species were restricted by the specific water environment of rocky outcrop, and species of the same functional type exhibited different water use strategies.