Carbon sink forests can fix atmospheric carbon dioxide and they play an important role in mitigating global warming. Research on the accumulation of soil carbon in carbon sink forests grown using different afforestation models in the South Asian subtropical region will contribute to our understanding of carbon sequestration by carbon sink forests. A single-factor randomized block design was used to investigate carbon sinks and three afforestation models. These were new afforestation (I), closed mountain afforestation (Ⅱ), and replanting (Ⅲ). Soil carbon accumulation and carbon sink function were also investigated. The results showed that the soil total carbon content was significantly different before and after the five-year study period. The soil carbon content in the 0-20 cm soil layer varied significantly among the afforestation models (P < 0.05), and the largest variation range was -0.861±1.893 g C/kg to 3.021±1.577 g C/kg. The multiple comparisons of soil organic carbon content showed that the soil organic carbon content in the 0-20 cm layer for the afforestation model was significantly different (P < 0.05) from the other two models. In 2016, after nearly five years of carbon sinking and afforestation, there were significant differences in the soil organic carbon contents between the different afforestation models (P < 0.05), especially in the topsoil. The soil carbon stocks in the 0-60 cm soil layer ranged between -2.233±3.540 and 8.670 ±2.342 Mg C/hm² for the different afforestation models and the difference in soil carbon stocks between new afforestation (I) and replanting (Ⅲ) was extremely significant (P < 0.01) after the carbon sink trees had been allowed to grow for 5 years. The soil carbon stocks also increased significantly. Between 2012 and 2016, the soil carbon sinks of the various afforestation models were ranked as follows:Ⅲ > Ⅱ > I, and the soils after closed mountain afforestation (Ⅱ) and replanting (Ⅲ) were significantly better carbon sinks than after model I. The afforestation model has significant effects on soil organic carbon accumulation and carbon sequestration in carbon sink forests. The main differences are caused by root decomposition, litter, and precipitation. The adoption of new afforestation models for the first five years does not improve soil organic carbon. Furthermore, accumulation and fixation do not improve organic carbon levels. Adopting a closed mountain afforestation model does improve soil organic carbon fixation, but does not increase the accumulation of organic carbon. However, the replanting model (Ⅲ) improves both soil carbon fixation and soil carbon accumulation.