[Objective] To analyze the carbon density of Pinus tabulaeformis and its influence factors in Longdong area in order to provide theoretical basis for the evaluation of the ecological environment of the loess hilly region. [Methods] The carbon density of Pinus tabulaeformis was estimated and the influence of ecological factors on carbon density was discussed by the methods of plot investigation and biomass measurement. [Results] The carbon content in different organs of P. tabulaeformis ranged from 48.58% to 53.54%, and the average carbon density decreased in the order of stem > branch > root > leaf > cone. The carbon content of leaf, branch, and root in shrub was 43.93%, 45.62% and 42.38%, respectively. The carbon content of above-ground and below-ground in herb was 43.04% and 39.77%. The carbon content of fresh litter and decomposing litter was 43.79% and 38.83%. The carbon density of vegetation layer decreased in the order of tree layer > herb layer > shrub layer. The average carbon content in the soil layer (0-100 cm) decreased gradually with the increase of soil depth, and the carbon density had significant difference in different layers, and that in 50-100 cm soil was the highest layer. The total carbon density of P. tabulaeformis ecosystem was 52.86 t/hm², and the vertical distribution were: soil layer(75.15%) > vegetation layer(24.14%) > litter layer(0.71%). [Conclusion] Ecological factors including average tree height, average diameter at breast height and canopy density showed highly significant correlation with the carbon density of different layers of P. tabulaeformis plantation, and undecomposed litter dry mass showed significant correlation with it. The average tree height, average diameter at breast height, canopy density, and undecomposed litter dry mass were primary factors on the carbon density of P. tabulaeformis ecosystem.