Evergreen broad-leaved forest is a typical vegetation type in subtropical China, with a complex ecosystem structure and important ecological functions and economic value. Coniferous and broad-leaved mixed forests play a significant role in subtropical evergreen broad-leaved forest ecosystems, contributing crucially to water and soil conservation and providing essential economic resources such as timber, medicinal herbs, and edible fungi. Conducting in-depth research on the water use characteristics of different tree species within these mixed forests is essential for enriching and advancing the understanding of subtropical evergreen broad-leaved forests. And vegetation transpiration is a key process in the water cycle of forest ecosystems, reflecting the water use characteristics of vegetation. Therefore, the determination of sap flow rate in tree stems is of great significance for the study of hydrological characteristics in a certain area. This study employed the Granier thermal dissipation probe method (Thermal Dissipation Probes, TDP) to monitor the variations in stem sap flow of dominant tree species-Schima superba, Pinus massoniana, and Castanopsis chinensis-within the transitional conifer-broadleaf mixed forest of Dinghushan Mountain in the southern subtropical region of China. The investigation included a comprehensive analysis of environmental factors such as relative humidity, atmospheric temperature, photosynthetically active radiation, total solar radiation, and precipitation. The main scientific questions explored are: 1. Are there any differences in stem sap flow rate, daily variation, and seasonal variation among different dominant tree species? 2. How do these differences vary with altitude? 3. What climatic factors have a critical impact on the sap flow rate of tree stems? Lastly, the results indicated that the diurnal patterns of stem sap flow showed either unimodal or bimodal curves, with higher flow rates during the day and lower rates at night, peaking around noon. Specifically, the peak sap flow density values were 42.08 g m^-2 s^-1for S. superba, 39.10 g m^-2 s^-1for P. massoniana, and 43.98 g m^-2 s^-1for C. chinensis. Significant differences in sap flow density were observed among the different tree species, with the average sap flow density ranking as C. chinensis > S. superba > P. massoniana. Additionally, there were variations in sap flow density among individuals of the same species, and different tree species exhibited varying degrees of responsiveness to different environmental factors. According to result, the sensitivity of different tree species to environmental factors varies and shows a trend of changing with the environment. In plot 1, atmospheric temperature is the primary environmental factor controlling the sap flow rate of S. superba, while total solar radiation is the critical factor controlling the sap flow rate of P. massoniana and C. chinensis. In plot 2 and 3, photosynthetically active radiation became the main environmental factor controlling the sap flow rate of various tree species. In summary, this study revealed the water use characteristics of different tree species in the transitional conifer-broadleaf mixed forest of Dinghushan Mountain and their relationship with environmental factors, providing a deeper understanding of water transport mechanisms in this ecosystem. These findings offer important references for the management and protection of forest ecosystems and lay a beneficial foundation for further research on the relationship between the water cycle and ecological balance in ecosystems. This study also provides new insights into the study of subtropical evergreen broad-leaved forests.