An improved viscoelastic spring lattice model was used to analyse the mechanical properties of polymer composites containing different microstructures, as exemplified by HTPB‐based solid propellants. A drop‐on‐demand structural model was programmed using the C language to simulate the real solid propellant microstructure. The results show that increasing the particle content has a positive effect on the tensile strength of the propellant, but is detrimental to the ductility. The increase in particle size decreases the maximum tensile strength of the material, reflecting the importance of the dewetting process in the microstructure analysis. Finally, the model accurately predicts that initial defects have a destructive effect on the mechanical properties of the materialThis article is protected by copyright. All rights reserved