It is a key issue in the improvement of plantation quality that how slow-growing Phoebe bournei species change their functional traits to adapt to the environment and achieve coexistence in the trade-off of resource acquisition and distribution after mixed with fast-growing Chinese fir species. In this paper, we selected Phoebe bournei pure forest and Phoebe bournei-Chinese fir mixed forest with the same initial conditions and similar ages in the Jindong State-owned Forest Farm in Qiyang County, Yongzhou City, Hunan Province as the research objects. Samples were collected in different seasons to calculate the responses of the leaf functional traits to the mixed pattern, and compared the differences of Phoebe bournei leaf functional traits between the mixed forest and the pure forest. We mainly studied 7 traits including the leaf thickness (LT), leaf area (LA), specific leaf area (SLA), leaf carbon content (LC), leaf nitrogen content (LN), leaf phosphorus content (LP), and nitrogen-phosphorus ratio (N:P) of Phoebe bournei leaves in both Phoebe bournei pure forest and forest mixed with Cunninghamia lanceolata in Jindong National Forest Farm in Hunan Province, and also discussed the correlations and plasticity of these traits. The results indicated that (1) comparing with Phoebe bournei pure forest, LA, SLA, LC, LN, and N:P of Phoebe bournei leaves in mixed forest increased by 16.78%, 8.50%, 3.12%, 21.38%, and 17.61%, respectively, while the leaf thickness and phosphorus content reduced by 8.80% and 25.87%. All of the functional traits had significant differences (p<0.05) except the LC. (2) Phoebe bournei hybridization led to significant changes of the correlations between LC, LN, LP and LT, LA, SLA traits. There is also a certain impact on LT, LA, SLA and their interactions as well as leaf C:N, C:P, N:P, which means that the correlations between the Phoebe bournei leaf functional traits have been adjusted adaptively. (3) The phenotypic plasticity index of the main Phoebe bournei leaf functional traits was distributed between 0.04 and 0.33. LT, LA, SLA and N:P were not sensitive to plasticity changes (PPI<0.20), while leaf nitrogen and phosphorus contents were more sensitive to plasticity changes (PPI> 0.20). And the order was LP > LN > N:P > LA > SLA > LT > LC. The results above showed that the mixed mode had non-significant effect on the plasticity changes of Phoebe bournei leaf morphological traits, which was not limited by growth space and light resource. However, the plasticity changes of LN and LP were sensitive to mixing. In this case, the growth process may be restricted by N and P. As there is also an obvious interspecific competition in mixed forest, nitrogen and phosphate fertilizers should be applied during the cultivation process. This research result will provide theoretical and data support for the future research on mixed afforestation model of fast-growing and precious tree species.