Influencing factors of soil organic carbon were more focus on national-scale to landscape-scale in the previous studies, while studies based on fine-scale such as stand-scale were less. Analysing the spatial distribution characteristics of soil organic carbon and assessing relative contributions of various influencing factors to soil organic carbon in stand-scale can provide a theoretical basis for the ecosystem carbon sink research and forest management. By using the the data of typical plots investigation which including 50 sample plots with area of 20 m × 20 m and sample determination, combining simple correlation analysis and boosted regression tree analysis, the relative contributions of possible influencing factors, including topography, stand characteristics, soil property and understory vegetation conditions to soil organic carbon content were evaluated in the aerially-seeded Pinus massoniana plantations in this study. Our results showed that the average soil organic carbon content in the aerially-seeded Pinus massoniana plantations was 10.22 g/kg at a soil depth of 0-10 cm and 6.64 g/kg at 10-20 cm, respectively. Soil organic carbon content decreased with soil depth. Coefficients of variation of soil organic carbon in those two soil layers were 59.5% and 60.1%, respectively, which belonged to moderate variation. The relative influence of soil property, stand characteristics, topography and understory vegetation conditions on soil organic carbon at the soil depth of 0-10 cm were 63.4%, 19.3%, 10.9%, and 6.4%, and were 60.4%, 21.9%, 10.6%, and 7.1% at the soil depth of 10-20 cm, which indicated that soil organic carbon contents were mainly affected by soil property conditions, followed by stand characteristics, topography, and understory vegetation conditions. Total nitrogen and total phosphorus were the main factors influencing soil organic carbon content, of which, total nitrogen had the largest contribution to soil organic carbon content at the soil depth of 0-10 cm, with a relative influence of 40.2%, while total phosphorus was the most important factor on soil organic carbon content at the soil depth of 10-20 cm, with a relative influence of 31.2%. The results of correlation significance test in simple correlation analysis and the fitting curve in boosted regression tree analysis all showed that total nitrogen, total phosphorus, and average diameter at breast height had significant positive correlations with soil organic carbon content at the two soil layers. Stand density and soil bulk density had significant negative correlations with soil organic carbon content at the depth of 0-10 cm. In addition, soil organic carbon content at the depth of 0-10 cm was higher in the place which more exposed to the sun. The other influencing factors related to soil organic carbon were not significant.