An artificial nitrogen deposition experiments in a typical steppe ecosystem in Inner Mongolia was conducted to study the long-term influences of nitrogen addition with different applying rates on the changing trends of different sections of the whole organic carbon pool. The results showed that plant aboveground living organic carbon pool size increased with the elevating rates of nitrogen addition, litter carbon pool size was also enhanced by the gradient increase of nitrogen deposition, though it had some what different responding curve compared with that of plant aboveground living organic carbon pool. Soil organic carbon pool size within the 0~10cm, 10~20cm, 20~30cm, and 30~70cm soil layers were not changed significantly along with the gradient of nitrogen deposition. As a consequence, belowground organic carbon pool and the total ecosystem organic carbon pool were not altered evidently in their size after the eight-year nitrogen addition with various rates.