In recent years, drought has caused increasing forest mortality at a global scale due to climate change, which draws wide attention. The main cause of drought-induced tree mortality is presumed to be out of the carbon-water balance in trees. This study investigated the effects of rainfall reduction on a secondary natural forest of Quercus aliena in Baotianman Mountains by imitating climate change. Three rainfall-intercepted plots were established in situ in a Q. aliena forest in Baotianman Mountain in April 2013, aiming to study the effects of reduced rainfall on the physiological relations of water-carbon, and growth of Q. aliena. The results showed that the predawn and midday water potential values of Q. aliena in the rainfall reduction plots were significantly lower than those of the control trees, and the lowest midday water potential value of rainfall-reduced Q. aliena was (-1.36±0.11)MPa. However, the water potential value which induced the xylem of Q. aliena lost 88% of hydraulic conductance was -3.19MPa, and the water potential value of Q. aliena at stomatal closure was -2.5MPa. Thus, rainfall reduction did not severely disturb the hydraulic architecture of Q. aliena in this region. After reduced rainfall, there were no significant differences in total nonstructural carbohydrates concentrations in leaves, phloem and xylem between rainfall-reduced trees and the control treatment. In summary, the rainfall-reduced Q. aliena trees did not show hydraulic failure or carbon starvation. However, the xylem vessel density and the leaf stomatal density of the rainfall reduction treated Q. aliena were significantly higher than those of control trees, and the xylem vessel diameter and the stomatal length were significantly smaller, which indicated that significant physiological and structural adaptations of rainfall-reduced Q. aliena trees occurred to cope with drought. During the relative drought, rainfall-intercepted Q. aliena showed a bimodal curve of the diurnal variation of stomatal conductance, while the control trees showed a unimodal curve. On the contrary, during the moist period, the diurnal dynamics of stomatal conductance of the rainfall-intercepted Q. aliena trees showed a monopeak curve similar to the control, and the peak value was significantly higher than that of control trees. There were no significant effects of reduced-rainfall on wood density, Huber value, specific leaf area and transversal growth of tree trunk of Q. aliena trees. Our results indicated that rainfall-reduced Q. aliena trees did not show hydraulic failure and carbon starvation, and the growth of Q. aliena was also not significantly influenced by reduced rainfall. However, their hydraulic structure showed adaptive adjustment to cope with more serious drought in future.