Accurate estimation of soil organic carbon density (SOCD) and storage plays a crucial role in evaluating the function of soil organic carbon in climate change. Taking four land-use types (bare land,grassland,cropland, and forest land) as examples, we explored the differences in SOCD of Mollisols profiles by using different methods of soil sampling (based on fixed soil depth and pedogenic horizon) and calculation of SOCD (based on equivalent soil volume (ESV) and equivalent soil mass (ESM)). The results showed there were significant differences in SOCD between the two different methods of soil sampling under the four land-use types. The order of SOCD based on fixed sampling depths and pedogenic horizon depended on land-use types. The values of ESV-based SOCD (0-30 cm) in forest land and grassland were significantly lower than those based on ESM method, whereas no significant impacts of the calculation methods on SOCD were observed for the deeper layers (100 and 200 cm). Our study suggests that appropriate methods of soil sampling and SOCD calculation should be considered according to given types of land uses and study purposes for estimation of soil storage. In addition, we can ignore the impact of the calculation method on SOCD in the deeper soil layers.