Abstract: In order to solve the problem of poor growth and even death caused by water shortage in the breeding of Phoebe bournei seedlings, this study used the 1-year-old P. bournei seedlings with different concentrations of exogenous spermidine to study the mitigation effect of spermidine on the drought stress of P. bournei seedlings. The results showed that treatment with exogenous spermidine can increased the net photosynthetic rate(P_n), stomatal conductance(G_s) and the activities of antioxidant enzymes(SOD, POD, CAT) of P. bournei to some extent, reduced the contents of proline(Pro) and malondialdehyde(MDA), and alleviated the influence of drought stress on P. bournei. Among them, spermidine at a concentration of 0.1 mmol/L had the best effect. After treatment, P_n and WUE were significantly higher than those of other treatment groups, especially in the late stage of drought stress. P_n and WUE were 82.1%, 123.7% higher than the control on the 32nd day of stress, the antioxidant enzymes SOD and CAT were 41.1% and 35.1% higher than the control, and Pro and MDA were 21.6% and 22.6% lower than the control, respectively.