Carbon dioxide (CO2), the main gas emitted from fossil burning, is the primary contributor to global warming. Circulating fluidized bed reactor (CFBR) is proved as an energy-efficient method for post-combustion CO2 cap-ture. The numerical simulation by computational fluid dynamics (CFD) is believed as a promising tool to study CO2 adsorption process in CFBR. Although three-dimensional (3D) simulations were proved to have better predicting performance with the experimental results, two-dimensional (2D) simulations have been widely re-ported for qualitative and quantitative studies on gas-solid behavior in CFBR for its higher computational effi-ciency recently. However, the discrepancies between 2D and 3D simulations have rarely been evaluated by detailed study. Considering that the differences between the 2D and 3D simulations will vary substantially with the changes of independent operating conditions, it is beneficial to lower computational costs to clarify the effects of dimensionality on the numerical CO2 adsorption runs under various operating conditions. In this work, the comparative analysis for CO2 adsorption in 2D and 3D simulations was conducted to enlighten the ef-fects of dimensionality on the hydrodynamics and reaction behaviors, in which the separation rate, species dis-tribution and hydrodynamic characteristics were comparatively studied for both model frames. With both accuracy and computational costs considered, the viable suggestions were provided in selecting appropriate model frame for the studies on optimization of operating conditions, which directly affect the capture and energy efficiencies of cyclic CO2 capture process in CFBR.