Organ-specific comparisons of carbon (C), nitrogen (N), and phosphorus (P) stoichiometrics and allometrics reflected the interfaces of the functional differentiation of plant tissues and the influence of environmental constraints. Here, we explored the seasonal constraints of organ-specific C, N, and P stoichiometrics and allometrics in a 25-year-old Cunninghamia lanceolata stand in Huitong, which located in subtropical China. Leaves, branches, and roots of trees covering a wide topographical gradient were collected at different seasons (January, April, July, October). We analyzed the seasonal dynamics of C, N, P content and C:N:P ecological stoichiometry in leaf, branch and root, and then revealed the variation、variation sources and allometric relationship of nutrient elements with different organs and months. The results showed that the C, N, and P contents and stoichiometries of the C. lanceolata varied in different organs and changed with seasons, reflecting a plastic seasonal variation and strong ontogenetic self-regulation. In all organs, the annual average N:P ratios (< 14) were much lower than the average level in China (16.3), suggesting that the growth of C. lanceolata in this region is relatively limited by N. The maximum C contents were observed in April for all organs, which was likely due to the increment of temperature in the growing season. The maximum C:N ratios were observed in July in all cases, indicating a relatively higher utilization rate of N in summer. In addition, the coefficients of variation (CVs) for N, P, C:N, C:P, and N:P were all higher than 30%, and the CVs for the P content and the N:P ratio in the branch were 65.04% and 62.41%, respectively. N and P of leaves, branches, and roots showed a positive correlation and an extremely significant allometric growth relationship between them(P < 0.001), with allometric exponents of 0.539, 0.617, and 0.721, respectively. This result demonstrated that growth rate changes significantly with an increase in nutrient concentration. The leaves and branches showed the highest N and P contents in October, which is possibly because of a temperature effect. The C:P ratios were the highest in winter. The changing trend of P showed an initial increase, followed by a decrease and then another increase. The highest N:P ratios in the leaves and roots were found in spring. The changing trends of C, N, and N:P were an initial increase, followed by a decrease and then another increase. By contrast, the C:N ratio changing trend was an initial decrease followed by an increase and then another decrease. C, N, and C:N showed extremely significant positive correlations (P < 0.001), and the N:P ratio showed a significantly positive correlation with leaves and roots. C and N were positively correlated, with a similar slope and significant allometric growth relationships (P < 0.05), which can be attributed to a difference in the environment of the leaves and roots. The highest annual average C, N, and P contents were measured in the leaves, with a mean value of (527.60±15.07), (10.55±1.89), and (2.13±0.31) g/kg, respectively. The greatest CVS for N, P, and N:P were found in the branches, proving that the absorption of N and P varies with seasons. The highest annual average C:N, C:P, and N:P were in the roots, with a mean value at (78.12±12.54), (619.46±48.23), and (7.13±3.57), respectively. The roots showed the highest CVs of C:N and C:P, indicating that the growth rate and nutrient use efficiency of the roots are strongly influenced by seasonal changes. Organ and season had an extremely significant effect on C content (P < 0.001), N, P, and N:P (P < 0.001). Furthermore, the influence of season for C:N reached an extremely significant level (P < 0.001), and the main effect of organ and the interaction between organ and month showed extremely significant effects for the C:P ratio (P < 0.001). The C and N contents in C. lanceolata changed with seasons, which is likely due to the change of temperature and precipitation in different seasons. The main influencing factor of C:P and N:P was organs, reflecting a different demand of N and P in each organ. Finally, the main influencing source of P and C:N was month, indicating that there are very different demands for these elements at different growth stages.