【Objective】 Soil CO₂ concentration is often higher than that of the atmosphere. Current studies on soil organic carbon mineralization are mostly conducted under conditions of increasing atmospheric or simulated atmospheric CO₂ concentration. This may lead to deviation of the results from the actual organic carbon mineralization process in the soil profile or impose some bias on indoor mineralization incubation experiments towards the “mineralization potential” rather than the actual mineralization rate. How and to what extent soil organic carbon mineralization is affected by high CO₂ concentrations in the soil profile? The lack of a clear answer to this question limits the comprehensive understanding of soil organic carbon stability. 【Method】 In this paper, an indoor mineralization incubation test was conducted with six CO₂concentration gradients of CK (400 µmol·mol^–1, atmospheric level), 800, 2 000, 4 000, 6 000, and 8 000 µmol·mol^–1, and three replicates were set for each treatment. The effects of different concentrations of CO₂ on the rate of soil organic carbon mineralization, cumulative mineralization, and active organic carbon fractions were investigated, and the extent to which CO₂ concentration and other influencing factors explained the cumulative mineralization was analyzed. 【Result】 The results showed that: 1) High concentration of CO₂(2 000-8 000 µmol·mol^–1) in soil significantly inhibited the mineralization of soil organic carbon, with the mineralization rate decreasing by 6.27%-45.61%, and the cumulative amount of mineralization decreased by 1.72%-40.82%; 2) Lower concentration of CO₂(800 µmol·mol^–1) in soil significantly promoted the mineralization of soil organic carbon, the mineralization rate increased by 4.38%-12.65%, and the cumulative mineralized amount increased by 17.37%-48.43%; 3) The CO₂ concentration in the soil effected the content of active organic carbon fractions. At a range of CO₂ concentrations, soil microbial biomass carbon (MBC) content increased significantly and dissolved organic carbon (DOC) content decreased significantly compared to CK. However, the content of easily oxidizable organic carbon (EOC) was not significantly changed; 4) The mineralization characteristics of organic carbon showed a significant negative correlation with CO₂ concentration, a significant positive correlation with DOC, a negative correlation with EOC, and no significant correlation with MBC; 5) Under the appropriate conditions of temperature and humidity, the contribution of CO₂ concentration to the cumulative mineralization of soil organic carbon reached 22.93%. 【Conclusion】 High CO₂ concentration significantly inhibited soil organic carbon mineralization by affecting the soil organic carbon readily available carbon source, which may be one of the important factors to maintain soil organic carbon stability.