Nanling Mountains are abundant in forest resources, which have the most well-preserved subtropical vegetation in the same latitude zone in the world and great carbon sequestration potential. However, the characteristics of total annual carbon budget and the monthly dynamics of different vegetation types with different altitudes in this region are still not clear. In this study, four vegetation types in Guangdong Nanling National Nature Reserve were selected, including valley evergreen broad-leaved forest, mountain evergreen broad-leaved forest, coniferous and broad-leaved mixed forest, and mountaintop evergreen broad-leaved brushwood. The integrated biosphere simulator (IBIS) was used to simulate the gross primary productivity (GPP), net primary productivity (NPP), net ecosystem productivity (NEP), and soil heterotrophic respiration (R_h) of different vegetation types in 2020. The model simulation ability was accurately verified with the observed NPP based on sample plot tally data, and the characteristics of total annual carbon budget and their monthly dynamic changes were analyzed. The results showed that the average of GPP, NPP, NEP and R_h of all vegetation types in Nanling respectively were 1.709, 0.718, 0.596 and 0.123 kg C m^-2 a^-1 in 2020. Among four vegetation types, the valley evergreen broad-leaved forest had the highest GPP, the mountain evergreen broad-leaved forest had the highest NPP and NEP, while the mountaintop evergreen broad-leaved brushwood had relatively low GPP, NPP and NEP. Different vegetation types in the Nanling showed monthly carbon sink (NEP>0). The monthly NPP and NEP of different vegetation types both showed bimodal curves with two peaks appearing in different months. The monthly R_h of different vegetation types showed unimodal curves with a single peak appearing in summer, with the lower value in winter, and valley evergreen broad-leaved forest had the highest R_h in summer when mountaintop evergreen broad-leaved brushwood had the lowest value. It was verified that the IBIS well simulated the carbon budget of different vegetation types in Nanling with the simulated values explained 93% of the actual situation of carbon budget, and the mean relative errors between the simulated values and the observed values of different vegetation types were in range of 1.16% to 6.07%. This study provided an important reference value for the evaluation of carbon sequestration capacity and the management of forest ecosystem resources in Nanling in subtropical zone of China.