The pocket concept describes aluminum-rich structure bounded by oxidizer particles in a solid propellant. Al particles inside a pocket tend to coalesce into a single agglomerate at the burning surface. However, detecting Al-rich microstructures in a real propellant is a challenging task. A calculation model based on cluster analysis and 3D model propellants is proposed to identify the Al-rich clusters and estimate the size distribution of the Al agglomerates. The effects of the parameters and propellant structures on the calculations were studied. The model was validated by comparing the modeled results with existing experimental data. The results demonstrate that the cluster structure of different hierarchies can be obtained by adjusting the user-prescribed parameters according to the reachability-plot. The present method is able to simulate the effect of the propellant microstructure on the Al-rich regions. In addition, the agglomerates of an HTPB (Hydroxyl-terminated polybutadiene) propellant is investigated under 1 MPa. The estimated size distribution of the agglomerates matches well with the experimental results. (C) 2019 The Combustion Institute. Published by Elsevier Inc. All rights reserved.