To reveal the dynamic patterns of carbon accumulation and allocation during the vegetation restoration process of Pinus tabulaeformis plantations at the subtropical to warm temperate transitional zone, this study focused on young and middle-aged Pinus tabulaeformis plantations in the southern Qinling Mountains, with grassland serving as the control. The variations in content of organic carbon and relative abundance of the stable carbon isotope (δ_¹³C) within the needle-litter-soil continuum were analyzed across these three vegetation types. The results showed that: (1) The content of organic carbon in the needles of the young forest was significantly higher than that of the middle-aged stand. However, there was no significant difference in δ_¹³C of the needles between young and middle-aged forests. Furthermore, neither the content of organic carbon nor δ_¹³C in the litter layer differed significantly across the three vegetation types. (2) Within the soil depth range of 0-30 cm, the organic carbon content (C) decreased with the increase in soil depth, and the average organic carbon content of both the middle-aged forest and the grassland was higher than that of the young forest. Soil δ_¹³C showed a pattern of young forest > middle-aged forest > grassland. δ_¹³C gradually increased as the soil depth increased but had no significant differences among different soil layers. (3) Soil δ_¹³C exhibited a negative correlation with lg C (P < 0. 05), and the soil carbon turnover rates of the three vegetation types followed the order of grassland > young forest > middle-aged forest. (4) δ_¹³C exhibited positive correlations across various soil layers (P < 0. 05). δ_¹³C in the 0-20 cm soil layer showed a negative correlation with that in the litter (P < 0. 05) but no significant correlation with that in needles.