The information of particle cluster dynamics is necessary for improving the performance of a circulating fluidized bed system. The main objective of this study is to compare the particle cluster diameters and concentrations from computational fluid dynamics simulation results between circulating fluidized bed riser and downer. The calculation methodologies are based on the concept of kinetic theory of granular flow and statistics. The mathematical model was verified by using the experimental dataset from literature and used for computing the particle cluster dynamics. In the circulating fluidized bed riser and downer, a dense and dilute core-annulus flow structures were obtained, respectively. The particle cluster in the circulating fluidized bed riser possessed more heterogeneity movements than that in the circulating fluidized bed downer. This can be explained by the system flow direction. About the particle cluster dynamics, the particle cluster diameters and concentrations in the circulating fluidized bed riser were higher than the ones in the downer. The calculated values were comparable to the empirical correlations. This confirms the validity of the calculation methodologies. Particle cluster dynamics and its example application inside circulating fluidized bed riser and downer were also discussed.