Study of the environmental effects of urbanization is important in terms of surface processes. The direct and potential effects of urbanization on the environment have become increasingly visible. With rapid global urbanization, studies involving the urban ecosystem have become more and more important. Urban soil, which is an important component of the urban ecosystem, is seriously affected by human activities. The impacts of human activities on urban soils, such as sealing, compaction, degradation, land filling, and mixing, are usually stronger than those on soils in non-urban environments. Soil sealing, defined here as land covered by impervious surfaces, such as housing, roads, or other pavements, is one of the main characteristics of urbanization and an indicator of changes in urban land cover. The exchange of material and energy between soil and other environmental compartments is reduced by artificial soil sealing in urban areas and this has a negative impact on soil functions. Soil organic carbon is an important indicator of soil function and quality, and is the most important carbon pool in terrestrial ecosystems. Therefore, studies on soil organic carbon transformations in urban soils could be used to evaluate the effects of urban soils on the wider environment. The resulting impacts on soil organic carbon stocks in urban areas, however, remain poorly characterized, especially for soils under impervious surfaces.In this paper, we established a soil sealing carbon cycle model to consider the factors that could affect the decomposition rate of soil organic carbon, such as the soil temperature, soil moisture, and other soil properties. The carbon flows between urban soil organic carbon pools could be accurately simulated using the model. We applied the model to simulate the decomposition process of soil organic carbon content in urban areas of Nanjing, which has recently experienced rapid urbanization, to reveal the impact of artificial soil sealing (including road pavements, residential areas, and squares) on soil organic carbon content from 1980 to 2010. By comparing soil organic carbon content between the sealed and open soils, we considered the impact of artificial soil sealing in urban areas on soil organic carbon. The results of the simulation can contributed to the study of the urban ecological environment during the process of urbanization and urban ecological construction. The major results are summarized as follows: (1) Soil sealing decreased soil organic carbon content significantly. The soil organic carbon content of the sealed urban soil was 6.7 g/kg in 2010 and was lower than the open soil by 54.7%. (2) Soils with low organic carbon content were mainly distributed in the rapidly urbanizing areas. (3) Previous research has estimated urban soil organic carbon storage by testing soils in open areas, because of the lack of organic carbon data from sealed soils. This has led to the overestimation of the urban soil carbon inventory. However, in a closed environment, the storage of the soil organic carbon pool would be significantly reduced. Through our model simulation, we found that the soil organic carbon pool was reduced by approximately 3.2×10⁵ t because of soil sealing in Nanjing from 1980 to 2010. The results of the simulation will contribute to the study of the urban ecological environment during the process of urbanization and urban ecological construction.