Abstract: The research focused on Xuzhou Platycladus orientalis plantation, to study the changes on carbon storage of the ecosystem and related mechanism in different stand ages(40, 48 and 55-yr-old)by applying biomass transformative equation and soil survey data. The results were as follows:(1)The percentage of carbon storage in tree layer rised with the increase of stand age. On contrast, the proportion of soil carbon storage was decreased. The carbon storage of the shrub, herb and floormass had no changes with the increase of stand age, while the whole ecosystem carbon storage rised with growing stand age. The total carbon storage of 55-yr-old stand was 109.55 t / hm², respectively 1.22 times and 1.09 times as much as that of 40-yr-old stand and 48-yr-old stand. Yet, this difference was mainly caused by the different carbon storage of tree layer and soil layer.(2)Fine root biomass indicated that the 1^st-3^rd root order biomass was found non-significantly changed. Although the 4^th-5^th root order and total biomass significantly decreased with stand age. Fine root morphology showed: compared with 40-yr-old stand, in the surface soil layer, the diameter of 5^th root order significantly decreased, while the root length of 5^th root order and specific root length of 1^st root order significantly increased in the 48-yr-old stand. The diameter and root length of 4^th root order, and the specific root length of 1^st root order significantly increased in the 55-yr-old stand. In the subsurface soil layer, the diameter of 3^rd root order and the root length of 4^th root order significantly increased, but the specific root length of 1^st and 2^nd root order significantly decreased in the 48-yr-old stand. The diameter of 3^rd - 5^th root order and the length of 5^th root order significantly increased, although the length of 3^rd root order and the specific root length of 1^st and 5^th root order significantly reduced in the 55-yr-old stand.(3)The relationship between the diameter of 3^rd root order and soil carbon storage was significant negatively correlated, but the diameter of 5^th root order positively correlated with total ecosystem carbon storage. The specific root length of 2^nd and 3^rd root order significant positively correlated with soil carbon storage, while the specific root length of 3^rd root order significant negatively correlated with tree layer carbon storage and litter layer carbon storage and ecosystem carbon storage. The biomass of 4^th and 5^th root order with litter layer carbon storage significant positively correlated, and with soil carbon storage in very significant negative correlation. Total fine root biomass significantly positive correlated with tree layer carbon storage and total carbon storage, and positively correlated with shrub layer carbon storage and herb layer carbon storage. As the results, the changes of fine root morphology and biomass may be one of the factors that cause the changes of ecosystem carbon storage.