Spatial distribution and its influence factors of topsoil (0-20 cm) organic carbon density (SOCD) of the Lower Reaches of Minjiang River were studied by the combination of traditional statistical analysis, gray related analysis, stepwise regression analysis and path analysis. SOCD ranged from 0.89 to 6.49 kg/m² with a mean value of 3.24 kg/m². Its overall distribution displayed irregular plaque-shaped, with a moderate spatial correlation, and SOCD was higher in the central low hilly than northeastern and eastern high hilly area. Among the influence factors, it showed extremely significant correlations with the land use, soil pH, topography, slope gradient and soil texture. Gray related analysis indicated that the highest correlation degree of SOCD with terrain, and followed by soil pH and soil parent material. Stepwise regression analysis combined with path analysis showed that terrain was the most significant influence factor, followed by soil parent material and pH. Therefore, terrain, soil parent material and pH were the main influence factors of topsoil organic carbon density in the lower reaches of Minjiang River.