Combustion performance optimization of solid rocket propellants critically enhances engine efficiency. Aluminum (Al) particles serve as prevalent metallic additives due to their high reactivity and energy density. A two-dimensional periodic sandwich homogenized steady-state combustion model was developed for AP/HTPB/Al propellants based on a five-step gas-phase reaction mechanism. Numerical simulations validated model reliability against experimental data. Increasing pressure from 0.2 MPa to 6.5 MPa transitions flame structures from premixed to diffusion combustion. Simultaneously, heat-release cores shift closer to the burning surface. At constant pressure, propellant burning rates rise significantly with higher ultra-fine aluminum (UFAL) content. UFAL concentration variations, however, produce distinct pressure sensitivity differences. This indicates a trade-off interval exists between achieving high burning rates and maintaining rate stability. These findings advance understanding of aluminum-containing composite propellant combustion behavior.