Since industrial revolution, a large amount of anthropogenic CO2 from fossil fuel combustion and deforestation has been emitted into atmosphere, and thus, the atmospheric CO2 concentration increased rapidly, while the delta 13C in atmospheric CO2 became lower and lower due to Suess effect. Therefore, the prediction of delta 13C is crucial for studying global changes. In order to make an accurate prediction, it is necessary to understand its historical variation. The dynamics of delta 13C in plants can sensitively reflect it. In this paper, the dynamics of delta 13C in atmospheric CO2 in the past 440 years in Aleitai, Xinjiang were reconstructed by using tree-ring delta 13C series and plant stable carbon isotope fractionation model. The results showed that atmospheric delta 13C value was relatively constant before 1,850 (R2 = 0.052), which was about -6.60@1000, while a sharp decrease in atmospheric delta 13C with an average of -7.02@1000 was found since 1,850 (R2 = 0.65). Compared with those from ice core bubbles, more fluctuations were found in atmospheric delta 13C derived from tree-ring series, possibly due to the higher resolution of the latter, and the difference of real atmospheric delta 13C between the growth site of the tree and the globe.