Research on the factors affecting soil organic carbon density is of great significance for regulating climate change and sustainable agricultural development. Previous studies have mainly explored the relationship between various factors (e.g., climate, altitude, soil physicochemical properties, etc.) and the influence of soil organic carbon density, but less involved in the interaction relationship between factors. Typical soil profiles were collected in Anhui Province to estimate the soil organic carbon density (SOCD) in the 0~10 cm, 10~20 cm, 20~30 cm and 30~100 cm soil horizons. The structural equation model was used to analyze the effects of climate, elevation, vegetation, soil water content, human activities and other environmental factors on SOCD. The results are as follows. In the 0~30 cm soil layer, SOCD show a gradually decreasing trend, and the average SOCD in the 0~10 cm, 10~20 cm and 20~30 cm soil layers were 2.09, 1.63 and 1.10 kg/m², respectively. The average SOCD of 30~100 cm soil layer is 4.46 kg/m². The spatial distribution of SOCD in the province gradually increased from north to south. The SOCD of 0~10 cm and 10~20 cm soil layer is higher than 5.00 kg/m^-2, mainly distributed in the Jianghuai hilly downland and the Riverine Plain. The areas with SOCD higher than 3.00 kg/m² in the 20~30 cm soil layer were distributed in the South Anhui hilly region. The high SOCD values of 30~100 cm are mainly distributed in the South Anhui hilly region. In the structural equation model of 0~10 cm, 10~20 cm and 20~30 cm soil layer, land use has the largest positive influence on SOCD, and the influence coefficients are 0.22, 0.20 and 0.22, respectively. The average annual temperature has the largest negative influence on SOCD, and the influence coefficients are -0.04 and -0.03. Annual rainfall was the most significant in 30~100 cm soil layer, but land use and NDVI were not significantly affected (p>0.05). Topography affects SOCD through four paths: land use, NDVI, annual precipitation and average annual temperature. Human footprint affected SOCD through NDVI, and the effect on NDVI reached a very significant level (p<0.001). The structural equation model established in this study initially explained the relationship between different environmental factors, and provid a theoretical basis for SOCD regulation and agricultural sustainable development.