The inhomogeneity of gas-solid flow will affect the hydrodynamic characteristics and the performance of the fluidized bed. In this paper, the distribution of the flexible filamentous particle clusters was experimentally studied. Specifically, the influences of riser height, superficial gas velocity and bed inventory on the fluidization behavior and particle cluster distribution in the riser were discussed. Moreover, a new algorithm to optimize cluster identification was employed. Furthermore, cluster shape was analyzed by two parameters of spherical and wide aspect ratio index. Last but not least, the orthogonal photograph shooting method and PIV measurement were employed for obtaining more information on the flow of flexible filamentous particles. The results showed that the riser height, superficial gas velocity and bed inventory have profound influence on the distribution characteristics of particle clusters. This work can provide a very important reference for the drying process of flexible filamentous particles and lays a foundation for the analysis of heat and mass transfer in the future. (C) 2018 Elsevier B.V. All rights reserved.