Organic carbon density (OCD) in different carbon pools of Pinus tabulaeformis forest ecosystem and its relationship with different geocentric factors are important for estimating forest carbon budgets, and helpful to understand forest carbon cycles.In this study, we established fifty sample plots at different site conditions using typical sampling method on the south slope of the Middle Qinling Mountains, where Pinus tabulaeformis is widely distributed. Organic carbon density in different carbon pools of Pinus tabulaeformis forest ecosystem and its relationship with different geocentric factors were estimated and analyzed. Our objective was to estimate OCD in different carbon pools of Pinus tabulaeformis forest ecosystem and its distribution on different geocentric factors, to understand the effects of geocentric factors on forest carbon budgets. The results showed that the total OCD of Pinus tabulaeformis forest ecosystem was 150.12 t/hm² in this region. The proportion of soil pool OCD was 56.74% and comprised the major part of the OCD of ecosystem. The OCD of litter pool was 2.66 t/hm², accounting for 1.77% of the ecosystem. Carbon density of vegetation pool was 62.29 t/hm²,taking up 41.49% of the OCD of ecosystem. The OCD of vegetation layer in this region was much higher than the average vegetation pool OCD of forest ecosystem in China, and mere carbon sequestrations are expected. The tree OCD was 61.22 t/hm², accounting 98.3% of the whole vegetation OCD. The OCD of shrub and herb were 0.65 t/hm² and 0.41 t/hm², accounting for 1.04% and 0.66% of the vegetation pool respectively. The OCD of different compositions of tree ranked as stem>branch>roots>leaf>bark. Effects of geocentric factors on the OCD of shrub and herb were insignificant. With the increase of elevation, the OCD of tree first increased and then decreased, peaking at 1500-1700 (a.s.l.). Variations of OCD in litter, soil and the ecosystem were insignificant. With the increase of slope gradient, the OCD of litter, soil and the ecosystem significantly decreased. In comparison, the OCD of tree first increased and then decreased, reaching its maximum on the slope gradient of 26-35°. The OCD of soil was higher in the lower slope compared with that of the middle and the upper slope, while the OCD of tree and the ecosystem was larger in the middle slope. Nevertheless, effects of slope position on the OCD of litter were slight. The OCD of tree at sun-facing slope appeared higher than that of back slope. While effects of slope aspect on the OCD of litter, soil layer and ecosystem were insignificant. It was concluded that effects of geocentric factors on the OCD of Pinus tabulaeformis forest ecosystem were mainly on the tree pool and soil pool on the south slope of the Middle Qinling Mountains. Effects of elevation, slope gradient, slope position, slope aspect were significant on tree pool, and effects of slope gradient, slope position were significant on soil pool. Geocentric factors should be considered in researches on forest ecosystem carbon cycles and estimation of carbon storage of forest ecosystem.